I am not new to shooting but just getting into the whole AR thing. My question is why are so many people shooting AR's in 7 twist. I understand the whole faster twist, longer bullet, better long range performance thing, but is everybody single loading them. The longest bullet that I can reasonably get in my mags is the 69 smk. It shoots great at 300 yards, at 600 it really dances in the wind. So is there a trick that I do not know about loading 75 - 80 grainers to mag length? Is the 69 SMK generally shot out to 600? If I want to shoot to 600 do I have to single load?
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Why a 7 twist AR?
- Thread starter Barrel Nut
- Start date
Re: Why a 7 twist AR?
77 SMK is an OTM bullet as is Nosler 77 and Hornady 75 BTHP.
75 A-max, 75 Berger VLD, 80 SMK are single load as OAL is in the 2.450" range.
RL-15, H4895, Varget or similar burn rate for the 75/77 OTM bullets.
77 SMK is an OTM bullet as is Nosler 77 and Hornady 75 BTHP.
75 A-max, 75 Berger VLD, 80 SMK are single load as OAL is in the 2.450" range.
RL-15, H4895, Varget or similar burn rate for the 75/77 OTM bullets.
Re: Why a 7 twist AR?
The heaviest bullets you can load to AR mag length are in the 75-77g category, as long as they aren't VLD type bullets. I shoot 77g SMKs and 77g Bergers myself.
Also, if you buy C-Products stainless steel mags, you can get an additional 0.020" COAL over traditional aluminum mags.
Yes, it is certainly advantageous to shoot heavier than 69g bullets to 600 yards. The higher the BC the better. And no, you don't have to single load. Just seat 'em to fit in your mags.
The heaviest bullets you can load to AR mag length are in the 75-77g category, as long as they aren't VLD type bullets. I shoot 77g SMKs and 77g Bergers myself.
Also, if you buy C-Products stainless steel mags, you can get an additional 0.020" COAL over traditional aluminum mags.
Yes, it is certainly advantageous to shoot heavier than 69g bullets to 600 yards. The higher the BC the better. And no, you don't have to single load. Just seat 'em to fit in your mags.
Re: Why a 7 twist AR?
The military uses the 7 twist to stabilize the longer tracer rounds. I'm guessing most people are not going to be shooting tracer rounds out of their personal AR's. 8 twist is all you will need for anything that you are going to load to mag-length anyway.
The military uses the 7 twist to stabilize the longer tracer rounds. I'm guessing most people are not going to be shooting tracer rounds out of their personal AR's. 8 twist is all you will need for anything that you are going to load to mag-length anyway.
Re: Why a 7 twist AR?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: shadow4</div><div class="ubbcode-body">The military uses the 7 twist to stabilize the longer tracer rounds. I'm guessing most people are not going to be shooting tracer rounds out of their personal AR's. 8 twist is all you will need for anything that you are going to load to mag-length anyway. </div></div>
Ummmm, not so much. The mil uses a 7 twisted tube because they shoot 62's out of a 14.5" tube. It's also handy for the 77's in a DMR gun. Tracer stability is an after thought.
That being said an 8 twisted tube in an 18 or 20ish' tube is a good choice for most everything.
Cheers,
Doc
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: shadow4</div><div class="ubbcode-body">The military uses the 7 twist to stabilize the longer tracer rounds. I'm guessing most people are not going to be shooting tracer rounds out of their personal AR's. 8 twist is all you will need for anything that you are going to load to mag-length anyway. </div></div>
Ummmm, not so much. The mil uses a 7 twisted tube because they shoot 62's out of a 14.5" tube. It's also handy for the 77's in a DMR gun. Tracer stability is an after thought.
That being said an 8 twisted tube in an 18 or 20ish' tube is a good choice for most everything.
Cheers,
Doc
Re: Why a 7 twist AR?
Not trying to start an argument but just to back up what I previously stated:
http://en.wikipedia.org/wiki/M16_rifle
"While the ideal twist rate for the SS109 projectile is 1:9 inch/1:229mm, a 1:7 inch/1:180mm twist rate was chosen to stabilize the much longer L110 tracer.
http://www.razoreye.net/mirror/ammo-oracle/AR15_com_Amm
racle_Mirror.htm
Q. What twist rate do I want for my rifle?
"Probably 1:9, but it depends on what kind of bullets you intend to shoot...................1:12 twist rifles cannot stabilize SS-109/M855 bullets and 1:7 twist rifles are slightly less accurate with lighter bullets and will often blow apart the thin jackets of lightweight varmint bullets. <span style="font-weight: bold"><span style="text-decoration: underline">The 1:7 twist is used by the military to stabilize the super-long L-110/M856 tracer bul</span>let</span> out to 800 yards, but unless your plans include shooting a significant amount of M856, the 1:9 twist rate is better suited for general use..........."
Also the the M16A2s were made with the 1/7 twist rate so I don't think it has much to do with the length of the barrel. I believe the M4 came after the M16A2
Not trying to start an argument but just to back up what I previously stated:
http://en.wikipedia.org/wiki/M16_rifle
"While the ideal twist rate for the SS109 projectile is 1:9 inch/1:229mm, a 1:7 inch/1:180mm twist rate was chosen to stabilize the much longer L110 tracer.
http://www.razoreye.net/mirror/ammo-oracle/AR15_com_Amm
racle_Mirror.htmQ. What twist rate do I want for my rifle?
"Probably 1:9, but it depends on what kind of bullets you intend to shoot...................1:12 twist rifles cannot stabilize SS-109/M855 bullets and 1:7 twist rifles are slightly less accurate with lighter bullets and will often blow apart the thin jackets of lightweight varmint bullets. <span style="font-weight: bold"><span style="text-decoration: underline">The 1:7 twist is used by the military to stabilize the super-long L-110/M856 tracer bul</span>let</span> out to 800 yards, but unless your plans include shooting a significant amount of M856, the 1:9 twist rate is better suited for general use..........."
Also the the M16A2s were made with the 1/7 twist rate so I don't think it has much to do with the length of the barrel. I believe the M4 came after the M16A2
Re: Why a 7 twist AR?
7 twist barrels are very common for HP Service Rifle competitors. Just about everyone shooting an AR for these matches loads 77 SMK's or 75 A-max at mag length for 200 and 300 yards and one of the many good 80's single-loaded for 600. It's a tried and true winning combination. 77's can also do very well at 600 if you don't want to single load. 23-24 grains of Reloader 15 or Varget pushing a 77 SMK should be very accurate and will get you a good ways past 600 in a good barrel. The ballistics are so good that it's almost like shooting a better caliber. A good 8 twist barrel will work for 77's also(and usually 80's too) but I like the 7 twist for my money.
Good luck,
Erik
7 twist barrels are very common for HP Service Rifle competitors. Just about everyone shooting an AR for these matches loads 77 SMK's or 75 A-max at mag length for 200 and 300 yards and one of the many good 80's single-loaded for 600. It's a tried and true winning combination. 77's can also do very well at 600 if you don't want to single load. 23-24 grains of Reloader 15 or Varget pushing a 77 SMK should be very accurate and will get you a good ways past 600 in a good barrel. The ballistics are so good that it's almost like shooting a better caliber. A good 8 twist barrel will work for 77's also(and usually 80's too) but I like the 7 twist for my money.
Good luck,
Erik
Re: Why a 7 twist AR?
Thanks for the information guys. I went to try some of my 69 SMK loads today. Nice here today wind running about 3-5 full effect. The 69 grain load shot great at 300 yards. Great for me is sub-MOA in this rifle. Went back to 600 and could not hit paper. Saw rounds impacting the berm short. I checked to make sure that I had the right dope on the scope and it was correct. I put 5 more minutes on and was still smacking in the mud. Started futzing with the scope and found that the reticle had stopped traveling. The knob turns and clicks but the reticle had just quit moving. It was very repeatable, I could turn the knobs and move it to a point then it would just quit. This point was just about 10 MOA from the optical center. I wonder how good the warranty service for Nikon is?
Thanks for the information guys. I went to try some of my 69 SMK loads today. Nice here today wind running about 3-5 full effect. The 69 grain load shot great at 300 yards. Great for me is sub-MOA in this rifle. Went back to 600 and could not hit paper. Saw rounds impacting the berm short. I checked to make sure that I had the right dope on the scope and it was correct. I put 5 more minutes on and was still smacking in the mud. Started futzing with the scope and found that the reticle had stopped traveling. The knob turns and clicks but the reticle had just quit moving. It was very repeatable, I could turn the knobs and move it to a point then it would just quit. This point was just about 10 MOA from the optical center. I wonder how good the warranty service for Nikon is?
Re: Why a 7 twist AR?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Barrel Nut</div><div class="ubbcode-body">Thanks for the information guys. I went to try some of my 69 SMK loads today. Nice here today wind running about 3-5 full effect. The 69 grain load shot great at 300 yards. Great for me is sub-MOA in this rifle. Went back to 600 and could not hit paper. Saw rounds impacting the berm short. I checked to make sure that I had the right dope on the scope and it was correct. I put 5 more minutes on and was still smacking in the mud. Started futzing with the scope and found that the reticle had stopped traveling. The knob turns and clicks but the reticle had just quit moving. It was very repeatable, I could turn the knobs and move it to a point then it would just quit. This point was just about 10 MOA from the optical center. I wonder how good the warranty service for Nikon is?
</div></div>
You have another problem. 69 SMK are not the best choice but can be shot to 600 yards.
Good luck
Jerry
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Barrel Nut</div><div class="ubbcode-body">Thanks for the information guys. I went to try some of my 69 SMK loads today. Nice here today wind running about 3-5 full effect. The 69 grain load shot great at 300 yards. Great for me is sub-MOA in this rifle. Went back to 600 and could not hit paper. Saw rounds impacting the berm short. I checked to make sure that I had the right dope on the scope and it was correct. I put 5 more minutes on and was still smacking in the mud. Started futzing with the scope and found that the reticle had stopped traveling. The knob turns and clicks but the reticle had just quit moving. It was very repeatable, I could turn the knobs and move it to a point then it would just quit. This point was just about 10 MOA from the optical center. I wonder how good the warranty service for Nikon is?
</div></div>
You have another problem. 69 SMK are not the best choice but can be shot to 600 yards.
Good luck
Jerry
Re: Why a 7 twist AR?
No you dont have to single load.
75 Hornady BTHP and 77 gr Sierra MK's can be loaded to mag length. And they shoot well with a 1-8 twist. Do I single load 80 gr Hornady's and 80 SMK'S for 600? Yes in a 1-7.7 twist Kreiger.... because they don't fit in a mag and the NRA across the course matches I shoot, 600yrds is shot prone slow fire. So you its easy to load them one at a time. Unlike the 200 & 300 yrd rapid fire that require a mag change. Otherwise I would be shooting an 8 twist with 75's or 77's (bthp's) at mag length. I don't see any reason to long seat if its not for competition. I mag length load everything that's for general paper punching. It keeps things simple and if you get in a hurry to load some bullets it won't be a bitch to shoot one at a time. My Burris 3-12 has enough travel to get out to 600 with a 69smk... just another point of view and some food for thought.
No you dont have to single load.
75 Hornady BTHP and 77 gr Sierra MK's can be loaded to mag length. And they shoot well with a 1-8 twist. Do I single load 80 gr Hornady's and 80 SMK'S for 600? Yes in a 1-7.7 twist Kreiger.... because they don't fit in a mag and the NRA across the course matches I shoot, 600yrds is shot prone slow fire. So you its easy to load them one at a time. Unlike the 200 & 300 yrd rapid fire that require a mag change. Otherwise I would be shooting an 8 twist with 75's or 77's (bthp's) at mag length. I don't see any reason to long seat if its not for competition. I mag length load everything that's for general paper punching. It keeps things simple and if you get in a hurry to load some bullets it won't be a bitch to shoot one at a time. My Burris 3-12 has enough travel to get out to 600 with a 69smk... just another point of view and some food for thought.
Re: Why a 7 twist AR?
The 75 grain hornady TAP I have at home is 2.25" overall. After looking at the 77 nosler, 77 smk and 75bthp bullets I think the hornady were the most uniform overall. Probably shoot the same though.
The 75 grain hornady TAP I have at home is 2.25" overall. After looking at the 77 nosler, 77 smk and 75bthp bullets I think the hornady were the most uniform overall. Probably shoot the same though.
Re: Why a 7 twist AR?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 2clicks</div><div class="ubbcode-body">
75 Hornady BTHP and 77 gr Sierra MK's can be loaded to mag length. </div></div>
The 75 hornady has a much higher bc than the 77 sierra.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 2clicks</div><div class="ubbcode-body">
75 Hornady BTHP and 77 gr Sierra MK's can be loaded to mag length. </div></div>
The 75 hornady has a much higher bc than the 77 sierra.
Re: Why a 7 twist AR?
The 62gr "green tip" M855 projo, and the M856 tracer projo. 1/7 is required to stabilize that long tracer bullet.
The 62gr "green tip" M855 projo, and the M856 tracer projo. 1/7 is required to stabilize that long tracer bullet.
Re: Why a 7 twist AR?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Erud</div><div class="ubbcode-body">7 twist barrels are very common for HP Service Rifle competitors.</div></div>
Maybe with the weekend competitors, but 1/8 is what the guys use who take the competition seriously. Plus, it's what the AMU uses.
FYI - my Rem 5R in 223 with 1/9 barrel shoots the 77-gr SMK perfectly, 0.33" group at 100-yards so far and I don't even have 100-rounds through it yet.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Erud</div><div class="ubbcode-body">7 twist barrels are very common for HP Service Rifle competitors.</div></div>
Maybe with the weekend competitors, but 1/8 is what the guys use who take the competition seriously. Plus, it's what the AMU uses.
FYI - my Rem 5R in 223 with 1/9 barrel shoots the 77-gr SMK perfectly, 0.33" group at 100-yards so far and I don't even have 100-rounds through it yet.
Re: Why a 7 twist AR?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Alpine 338</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Erud</div><div class="ubbcode-body">7 twist barrels are very common for HP Service Rifle competitors.</div></div>
Maybe with the weekend competitors, but 1/8 is what the guys use who take the competition seriously. Plus, it's what the AMU uses.
FYI - my Rem 5R in 223 with 1/9 barrel shoots the 77-gr SMK perfectly, 0.33" group at 100-yards so far and I don't even have 100-rounds through it yet. </div></div>
Take it easy there champ, I was just offering my opinion based on my personal experience and that of guys I shoot with. While I am not shooting for the AMU, I like to think that I take SR shooting fairly seriously and have done a fair amount of it. In the rifles I've owned and the ones I see at matches, 7 twist is definitely the most common with plenty of 7.7's and 8's mixed in as well. Even the occasional 6.5 for the guys still experimenting with the various 90's. They can all work just fine if you know how to shoot. 1 in 9 is getting a little slow, but if it works for you and your 5R then I'm happy for you. I like the 1 in 7 twist personally, if that's ok with you....
Thanks,
Erik
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Alpine 338</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Erud</div><div class="ubbcode-body">7 twist barrels are very common for HP Service Rifle competitors.</div></div>
Maybe with the weekend competitors, but 1/8 is what the guys use who take the competition seriously. Plus, it's what the AMU uses.
FYI - my Rem 5R in 223 with 1/9 barrel shoots the 77-gr SMK perfectly, 0.33" group at 100-yards so far and I don't even have 100-rounds through it yet. </div></div>
Take it easy there champ, I was just offering my opinion based on my personal experience and that of guys I shoot with. While I am not shooting for the AMU, I like to think that I take SR shooting fairly seriously and have done a fair amount of it. In the rifles I've owned and the ones I see at matches, 7 twist is definitely the most common with plenty of 7.7's and 8's mixed in as well. Even the occasional 6.5 for the guys still experimenting with the various 90's. They can all work just fine if you know how to shoot. 1 in 9 is getting a little slow, but if it works for you and your 5R then I'm happy for you. I like the 1 in 7 twist personally, if that's ok with you....
Thanks,
Erik
Re: Why a 7 twist AR?
Erik,
No offence meant, and not to beat a dead horse, but a lot of folks think that 1/7 twist is the best since that's what the Military uses in the M16A2 and M4's. I think most experienced shooters, as you, probably realize that the 1/7 twist was adopted to stabalize the M856 tracer round because of its length (not weight). And that if not for that tracer round, they (the U.S. Military) would have probably went with 1/9 as some of our NATO alies did initialy. I guess my point being, anything more then 1/8 twist is not needed to stabalize most match bullets up to 80-gr., and in some cases, 1/7 will over-stablize a lighter/shorter bullet, thus causing long range accuracy to suffer. Yes, 1/7 works very well for SR, and is very common in SR competition. I was just trying to point out that most of the top competetors mostly use 1/8.
Again, not trying to disagree with you or offend you.
Take care,
Andy
Erik,
No offence meant, and not to beat a dead horse, but a lot of folks think that 1/7 twist is the best since that's what the Military uses in the M16A2 and M4's. I think most experienced shooters, as you, probably realize that the 1/7 twist was adopted to stabalize the M856 tracer round because of its length (not weight). And that if not for that tracer round, they (the U.S. Military) would have probably went with 1/9 as some of our NATO alies did initialy. I guess my point being, anything more then 1/8 twist is not needed to stabalize most match bullets up to 80-gr., and in some cases, 1/7 will over-stablize a lighter/shorter bullet, thus causing long range accuracy to suffer. Yes, 1/7 works very well for SR, and is very common in SR competition. I was just trying to point out that most of the top competetors mostly use 1/8.
Again, not trying to disagree with you or offend you.
Take care,
Andy
Re: Why a 7 twist AR?
The decision to go with a 1:7 twist for carbines is related to the barrel length. For shorter barrel rifles, the bullets do not achieve the higher velocities that could be produced out of the 20" M16s, and there was concern about inadequate stabilization out of a 1:9 twist. As a result, it was determined that 1:7 twist could properly stabilize the M855/M856 ammunition out of the 14.5" M4 barrels.
In terms of non-SBR lengths, the tighter rifling is advantageous for heavier bullets, as has been pointed out already.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: glock24</div><div class="ubbcode-body">The heaviest bullets you can load to AR mag length are in the 75-77g category, as long as they aren't VLD type bullets. I shoot 77g SMKs and 77g Bergers myself.
</div></div>
The 87gr PRL load that the military developed in conjunction with Barnes is now the king for AR magazine fitment. I can't wait to get my hands on that bad boy.
![attachment.php](http://[url="http://www.sniperinfo.com/forum/attachment.php?attachmentid=211&d=1280446871"]http://www.sniperinfo.com/forum/attachment.php?attachmentid=211&d=1280446871[/url])
The decision to go with a 1:7 twist for carbines is related to the barrel length. For shorter barrel rifles, the bullets do not achieve the higher velocities that could be produced out of the 20" M16s, and there was concern about inadequate stabilization out of a 1:9 twist. As a result, it was determined that 1:7 twist could properly stabilize the M855/M856 ammunition out of the 14.5" M4 barrels.
In terms of non-SBR lengths, the tighter rifling is advantageous for heavier bullets, as has been pointed out already.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: glock24</div><div class="ubbcode-body">The heaviest bullets you can load to AR mag length are in the 75-77g category, as long as they aren't VLD type bullets. I shoot 77g SMKs and 77g Bergers myself.
</div></div>
The 87gr PRL load that the military developed in conjunction with Barnes is now the king for AR magazine fitment. I can't wait to get my hands on that bad boy.
Re: Why a 7 twist AR?
why is 75AMAX longer than 77SMK? dont understand why 75AMAX has
to be single-loaded
why is 75AMAX longer than 77SMK? dont understand why 75AMAX has
to be single-loaded
Re: Why a 7 twist AR?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BERTMAN77MK2</div><div class="ubbcode-body">why is 75AMAX longer than 77SMK? </div></div>
Because it's longer than a 77smk. Little plastic tip, overall design of the bullet etc.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BERTMAN77MK2</div><div class="ubbcode-body">why is 75AMAX longer than 77SMK? </div></div>
Because it's longer than a 77smk. Little plastic tip, overall design of the bullet etc.
Re: Why a 7 twist AR?
shooting threw vegetation,window,ETC or anything between barrel and target that disturbs the projectiles gyroscopic stabilization on its normal path to the target the 7 twist will do the job better than a 1-9/1-8 with 77 grain projectiles..7 twist "could" also help keep the projectile on target "stable" threw the transonic flight better than 1-9/1-8 ..
7 twist will gyroscopic over stabilize shorter rounds. accuracy only hampered by the bullets quality and balance from overstabalazation. More spin drift will also result,But the shorter distance using lighter projectiles will nullify the amount of drift,
Less quality bullets will need closer to optimum stabilization for the weight;length of the projectile..If accuracy is a concern.
(In short) the 1-7 is a better option to get the projectile to its intended impact point in combat.
shooting threw vegetation,window,ETC or anything between barrel and target that disturbs the projectiles gyroscopic stabilization on its normal path to the target the 7 twist will do the job better than a 1-9/1-8 with 77 grain projectiles..7 twist "could" also help keep the projectile on target "stable" threw the transonic flight better than 1-9/1-8 ..
7 twist will gyroscopic over stabilize shorter rounds. accuracy only hampered by the bullets quality and balance from overstabalazation. More spin drift will also result,But the shorter distance using lighter projectiles will nullify the amount of drift,
Less quality bullets will need closer to optimum stabilization for the weight;length of the projectile..If accuracy is a concern.
(In short) the 1-7 is a better option to get the projectile to its intended impact point in combat.
Re: Why a 7 twist AR?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BERTMAN77MK2</div><div class="ubbcode-body">why is 75AMAX longer than 77SMK? dont understand why 75AMAX has
to be single-loaded </div></div>
SECANT VS TANGENT two different designs,The sleek rounds are normally longer in length.
The 75 amax loaded to mag length for an AR15 will set back in the case beyond the radius and cause a undercut ..(75 amax its less rounded and sleeker)
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BERTMAN77MK2</div><div class="ubbcode-body">why is 75AMAX longer than 77SMK? dont understand why 75AMAX has
to be single-loaded </div></div>
SECANT VS TANGENT two different designs,The sleek rounds are normally longer in length.
The 75 amax loaded to mag length for an AR15 will set back in the case beyond the radius and cause a undercut ..(75 amax its less rounded and sleeker)
Re: Why a 7 twist AR?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: kraigWY</div><div class="ubbcode-body">Ask the Army, they seem to have figured it out.</div></div>
Since M855 is steel-cored (green tip) ammo, its aerodynamic stability may be inherently different than a 62-grain bullet made with a lead core. A longer bullet is generally less stable than a shorter one of the same weight; since steel is less dense than lead, a steel-cored bullet of the same weight is probably longer and less stable - thus the need for a higher spin rate.
In addition, steel-cored ammo may have a shifted center of mass, leading to lower aerodynamic stability. A dart is stable because the center of mass is far to the front (because of the weighted spike) and center of pressure is far to the rear (the reason for the tail feathers). If you move the center of mass of a dart to the rear, it becomes less stable in flight. The same is true of bullets.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: kraigWY</div><div class="ubbcode-body">Ask the Army, they seem to have figured it out.</div></div>
Since M855 is steel-cored (green tip) ammo, its aerodynamic stability may be inherently different than a 62-grain bullet made with a lead core. A longer bullet is generally less stable than a shorter one of the same weight; since steel is less dense than lead, a steel-cored bullet of the same weight is probably longer and less stable - thus the need for a higher spin rate.
In addition, steel-cored ammo may have a shifted center of mass, leading to lower aerodynamic stability. A dart is stable because the center of mass is far to the front (because of the weighted spike) and center of pressure is far to the rear (the reason for the tail feathers). If you move the center of mass of a dart to the rear, it becomes less stable in flight. The same is true of bullets.
Re: Why a 7 twist AR?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: USACS</div><div class="ubbcode-body">The decision to go with a 1:7 twist for carbines is related to the barrel length. </div></div>
Understood.
Question to anyone: what ammunition is best suited to 18.0" of 1:7.3 twist?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: USACS</div><div class="ubbcode-body">The decision to go with a 1:7 twist for carbines is related to the barrel length. </div></div>
Understood.
Question to anyone: what ammunition is best suited to 18.0" of 1:7.3 twist?
Re: Why a 7 twist AR?
+1 ASM-1 YOU ARE RIGHT ON THE MONEY WITH THAT,---EVEN THOUGH i LIKE THE 1/8" TWIST
+1 ASM-1 YOU ARE RIGHT ON THE MONEY WITH THAT,---EVEN THOUGH i LIKE THE 1/8" TWIST
Re: Why a 7 twist AR?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: H2O MAN</div><div class="ubbcode-body">
Question to anyone: what ammunition is best suited to 18.0" of 1:7.3 twist? </div></div>
I assume you mean 223?
Whatever works best in it. Some shoot 52-77 well, some only like heavy, depends on lots of things. My 1:7 only seems to like 69-77. 55's are 2" or greater at 100. By contrast my 1:8's will shoot incredibly well with anything from 52-77.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: H2O MAN</div><div class="ubbcode-body">
Question to anyone: what ammunition is best suited to 18.0" of 1:7.3 twist? </div></div>
I assume you mean 223?
Whatever works best in it. Some shoot 52-77 well, some only like heavy, depends on lots of things. My 1:7 only seems to like 69-77. 55's are 2" or greater at 100. By contrast my 1:8's will shoot incredibly well with anything from 52-77.
Re: Why a 7 twist AR?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BCP</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: H2O MAN</div><div class="ubbcode-body">
Question to anyone: what ammunition is best suited to 18.0" of 1:7.3 twist? </div></div>
I assume you mean 223?
Whatever works best in it. Some shoot 52-77 well, some only like heavy, depends on lots of things. My 1:7 only seems to like 69-77. 55's are 2" or greater at 100. By contrast my 1:8's will shoot incredibly well with anything from 52-77. </div></div>
Yeah, 5.56mm/.223
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BCP</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: H2O MAN</div><div class="ubbcode-body">
Question to anyone: what ammunition is best suited to 18.0" of 1:7.3 twist? </div></div>
I assume you mean 223?
Whatever works best in it. Some shoot 52-77 well, some only like heavy, depends on lots of things. My 1:7 only seems to like 69-77. 55's are 2" or greater at 100. By contrast my 1:8's will shoot incredibly well with anything from 52-77. </div></div>
Yeah, 5.56mm/.223
Re: Why a 7 twist AR?
1:7 because its a shorter barrel? That's a new one. The original tracer answer is historically correct. For civies, barrel twist simply needs to be matched to the bullet you are shooting. Generally, weight is a proxy for twist: heavier bullets require faster twists. But, as pointed out, the bullet profile matters and VLD-type bullets (secant) require faster twists than tangent ogives.
In 223, an 80grain bullet is generally considered the best long-range round (non-mag length) and a 1:8 twist is the minimum required with 1:7 providing a bit more flexibility in bullet choices. If you want to shoot a 90gr vld, then a 1:6.5 twist is required, but most folks gave up on the 90gr bullet in 223 a long time ago because it didn't really improve on the 80 grain.
1:7 because its a shorter barrel? That's a new one. The original tracer answer is historically correct. For civies, barrel twist simply needs to be matched to the bullet you are shooting. Generally, weight is a proxy for twist: heavier bullets require faster twists. But, as pointed out, the bullet profile matters and VLD-type bullets (secant) require faster twists than tangent ogives.
In 223, an 80grain bullet is generally considered the best long-range round (non-mag length) and a 1:8 twist is the minimum required with 1:7 providing a bit more flexibility in bullet choices. If you want to shoot a 90gr vld, then a 1:6.5 twist is required, but most folks gave up on the 90gr bullet in 223 a long time ago because it didn't really improve on the 80 grain.
Re: Why a 7 twist AR?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: One-Eyed Jack</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: kraigWY</div><div class="ubbcode-body">Ask the Army, they seem to have figured it out.</div></div>
Since M855 is steel-cored (green tip) ammo, its aerodynamic stability may be inherently different than a 62-grain bullet made with a lead core. A longer bullet is generally less stable than a shorter one of the same weight; since steel is less dense than lead, a steel-cored bullet of the same weight is probably longer and less stable - thus the need for a higher spin rate.
In addition, steel-cored ammo may have a shifted center of mass, leading to lower aerodynamic stability. A dart is stable because the center of mass is far to the front (because of the weighted spike) and center of pressure is far to the rear (the reason for the tail feathers). If you move the center of mass of a dart to the rear, it becomes less stable in flight. The same is true of bullets. </div></div>plus i learned this from FN back in the 80's the stress of 1/7 twist works the jacket / canalure point hard for breakage with ss-109 -the jacket is designed break into two parts in a fluidity body -with a 20'' barrel ... seen this at ft.benning back in 80's with fn people ...
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: One-Eyed Jack</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: kraigWY</div><div class="ubbcode-body">Ask the Army, they seem to have figured it out.</div></div>
Since M855 is steel-cored (green tip) ammo, its aerodynamic stability may be inherently different than a 62-grain bullet made with a lead core. A longer bullet is generally less stable than a shorter one of the same weight; since steel is less dense than lead, a steel-cored bullet of the same weight is probably longer and less stable - thus the need for a higher spin rate.
In addition, steel-cored ammo may have a shifted center of mass, leading to lower aerodynamic stability. A dart is stable because the center of mass is far to the front (because of the weighted spike) and center of pressure is far to the rear (the reason for the tail feathers). If you move the center of mass of a dart to the rear, it becomes less stable in flight. The same is true of bullets. </div></div>plus i learned this from FN back in the 80's the stress of 1/7 twist works the jacket / canalure point hard for breakage with ss-109 -the jacket is designed break into two parts in a fluidity body -with a 20'' barrel ... seen this at ft.benning back in 80's with fn people ...
Re: Why a 7 twist AR?
When I started HP comp, I had a 1:8 Wilson barreled SR.
I shot a pretty standard load of an 80 SMK or a-max, with 24.0 RL-15 for the 600 yard stage.
I was new and didn't realize that the occasional flyers that I got were caused by insufficient bullet stability.
Everyone said it was me (like my rifle and ammo are infallible).
This had plagued me for over a year!
At one particular practice day I had several "off call" shots, and even a miss up at the top of the target.
I knew that I was shooting well that day, and 300 went very good for me so I figured that something must be up.
I bumped that load up to 24.5, and I never saw another flyer again!
I wasted a lot of time, and had a lot of frustration caused by that 1:8 twist (I did accurately measure its actual twist rate).
I had to push my load to the maximum to get it to stabilize the 80's.
That barrel was probably more accurate than my current 1:7 Kreiger is now, but I didn't want to be that close to the margins again.
My next barrel will likely be a 1:7.7 Kreiger.
If you push your 80's really fast, then you can get away with less twist rate (like the AMU).
If you shoot mouse farts at low density altitudes, you'd better get a 1:7.
A 1:7.7 will likely serve most folks the best.
Moral of story:
It's better to err on the side of stability.
People who speak in absolutes are either:
A) full of shit.
B) Trying to sell you something.
I learned all this the hard way.
When I started HP comp, I had a 1:8 Wilson barreled SR.
I shot a pretty standard load of an 80 SMK or a-max, with 24.0 RL-15 for the 600 yard stage.
I was new and didn't realize that the occasional flyers that I got were caused by insufficient bullet stability.
Everyone said it was me (like my rifle and ammo are infallible).
This had plagued me for over a year!
At one particular practice day I had several "off call" shots, and even a miss up at the top of the target.
I knew that I was shooting well that day, and 300 went very good for me so I figured that something must be up.
I bumped that load up to 24.5, and I never saw another flyer again!
I wasted a lot of time, and had a lot of frustration caused by that 1:8 twist (I did accurately measure its actual twist rate).
I had to push my load to the maximum to get it to stabilize the 80's.
That barrel was probably more accurate than my current 1:7 Kreiger is now, but I didn't want to be that close to the margins again.
My next barrel will likely be a 1:7.7 Kreiger.
If you push your 80's really fast, then you can get away with less twist rate (like the AMU).
If you shoot mouse farts at low density altitudes, you'd better get a 1:7.
A 1:7.7 will likely serve most folks the best.
Moral of story:
It's better to err on the side of stability.
People who speak in absolutes are either:
A) full of shit.
B) Trying to sell you something.
I learned all this the hard way.
Re: Why a 7 twist AR?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: H2O MAN</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: USACS</div><div class="ubbcode-body">The decision to go with a 1:7 twist for carbines is related to the barrel length. </div></div>
Understood.
Question to anyone: what ammunition is best suited to 18.0" of 1:7.3 twist? </div></div>
I'd start with the wonderful 77 SMK, rem 7 1/2, and whatever cases you like best that have consistent neck tension.
Load to 2.26" OAL.
Work up to a 100% load density (non compressed) if you can, with RL-15, or varget.
I ended up around 24.0 with either.
I'd go with varget if this isn't for competition, because it behaves better with temp changes.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: H2O MAN</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: USACS</div><div class="ubbcode-body">The decision to go with a 1:7 twist for carbines is related to the barrel length. </div></div>
Understood.
Question to anyone: what ammunition is best suited to 18.0" of 1:7.3 twist? </div></div>
I'd start with the wonderful 77 SMK, rem 7 1/2, and whatever cases you like best that have consistent neck tension.
Load to 2.26" OAL.
Work up to a 100% load density (non compressed) if you can, with RL-15, or varget.
I ended up around 24.0 with either.
I'd go with varget if this isn't for competition, because it behaves better with temp changes.
Re: Why a 7 twist AR?
I'm using a 1:7.7 twist Krieger on my CLE Service rifle. Optimal twist for 77 SMKs across the course.
-David
Edgewood, NM
I'm using a 1:7.7 twist Krieger on my CLE Service rifle. Optimal twist for 77 SMKs across the course.
-David
Edgewood, NM
Re: Why a 7 twist AR?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Barrel Nut</div><div class="ubbcode-body">Thanks for the information guys. I went to try some of my 69 SMK loads today. Nice here today wind running about 3-5 full effect. The 69 grain load shot great at 300 yards. Great for me is sub-MOA in this rifle. Went back to 600 and could not hit paper. Saw rounds impacting the berm short. I checked to make sure that I had the right dope on the scope and it was correct. I put 5 more minutes on and was still smacking in the mud. Started futzing with the scope and found that the reticle had stopped traveling. The knob turns and clicks but the reticle had just quit moving. It was very repeatable, I could turn the knobs and move it to a point then it would just quit. This point was just about 10 MOA from the optical center. I wonder how good the warranty service for Nikon is?
</div></div>
That's not a bullet problem, that's a scope shim problem.
Nikon is probable saving your reticle from you twisting it too hard and stripping the vertical adjustment.
That said, shadow4 is right. The 1-7" was chosen over the 1-9" twist to stabilize the tracer round (M856) that was to accompany the new 62 gr. round (M855){formerly SS109}. A 1-9" will stabilize anything you can feed from a magazine <span style="font-style: italic">if you push them hard</span>. With a 1-8" twist you can stabilize up around 80 gr.'s if you don't push them as hard. The 1-7" will stabilize up to a 90 gr. bullet without having to push them hard. Generally speaking any VLD type or A-max longer than a 68 gr. will require single feeding. If you go with a 1-7" twist, you can single feed at lower velocities and still get very predictable stability with the longer rounds.
The biggest problem with being under-twisted is stability at long range. At lower altitudes, bullets are more adversely affected as they come down in speed through the transonic range. They don't fall out of the sky, but they do lose accuracy. Over-twisting uses the gyroscopic forces to increase the chances of re-stabilizing, or more usually, decreasing time to re-stabilize the bullet once the transonic range has been reached.
That's why most people use a 1-7" twist. It handles bullets down to <span style="text-decoration: line-through">69</span> 60gr. just fine, but is more oriented towards single feeding of the higher weight/BC .22 cal. bullets out there.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Barrel Nut</div><div class="ubbcode-body">Thanks for the information guys. I went to try some of my 69 SMK loads today. Nice here today wind running about 3-5 full effect. The 69 grain load shot great at 300 yards. Great for me is sub-MOA in this rifle. Went back to 600 and could not hit paper. Saw rounds impacting the berm short. I checked to make sure that I had the right dope on the scope and it was correct. I put 5 more minutes on and was still smacking in the mud. Started futzing with the scope and found that the reticle had stopped traveling. The knob turns and clicks but the reticle had just quit moving. It was very repeatable, I could turn the knobs and move it to a point then it would just quit. This point was just about 10 MOA from the optical center. I wonder how good the warranty service for Nikon is?
</div></div>
That's not a bullet problem, that's a scope shim problem.
Nikon is probable saving your reticle from you twisting it too hard and stripping the vertical adjustment.
That said, shadow4 is right. The 1-7" was chosen over the 1-9" twist to stabilize the tracer round (M856) that was to accompany the new 62 gr. round (M855){formerly SS109}. A 1-9" will stabilize anything you can feed from a magazine <span style="font-style: italic">if you push them hard</span>. With a 1-8" twist you can stabilize up around 80 gr.'s if you don't push them as hard. The 1-7" will stabilize up to a 90 gr. bullet without having to push them hard. Generally speaking any VLD type or A-max longer than a 68 gr. will require single feeding. If you go with a 1-7" twist, you can single feed at lower velocities and still get very predictable stability with the longer rounds.
The biggest problem with being under-twisted is stability at long range. At lower altitudes, bullets are more adversely affected as they come down in speed through the transonic range. They don't fall out of the sky, but they do lose accuracy. Over-twisting uses the gyroscopic forces to increase the chances of re-stabilizing, or more usually, decreasing time to re-stabilize the bullet once the transonic range has been reached.
That's why most people use a 1-7" twist. It handles bullets down to <span style="text-decoration: line-through">69</span> 60gr. just fine, but is more oriented towards single feeding of the higher weight/BC .22 cal. bullets out there.
Re: Why a 7 twist AR?
A bullet in flight is a lot like a spiraling football.
There are restoring forces that make it want to go "pointy end first".
This is caused by a combination of aerodynamic forces, and gyroscopic precession.
Being spun at minimal RPM for adequate stability will allow it to track within your ballistic arc nearly perfectly.
Over spun and it wants to hold it's gyroscopic heading, and needs greater restoring forces to bring the angle of attack back to zero.
The bullet tip will actually hunt around in a tiny circle when changes in AOA are encountered, minimizing at zero AOA.
The more spin, the more pronounced this is.
If you can, watch a spiraling football in slow-motion and you can see it in action.
Although a football is not the best analogy, it does highlight these gyroscopic pressesive forces at work as they pertain to long range bullet flight, and why being spun just enough is usually best for long range accuracy.
A bullet in flight is a lot like a spiraling football.
There are restoring forces that make it want to go "pointy end first".
This is caused by a combination of aerodynamic forces, and gyroscopic precession.
Being spun at minimal RPM for adequate stability will allow it to track within your ballistic arc nearly perfectly.
Over spun and it wants to hold it's gyroscopic heading, and needs greater restoring forces to bring the angle of attack back to zero.
The bullet tip will actually hunt around in a tiny circle when changes in AOA are encountered, minimizing at zero AOA.
The more spin, the more pronounced this is.
If you can, watch a spiraling football in slow-motion and you can see it in action.
Although a football is not the best analogy, it does highlight these gyroscopic pressesive forces at work as they pertain to long range bullet flight, and why being spun just enough is usually best for long range accuracy.
Re: Why a 7 twist AR?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hamilton</div><div class="ubbcode-body">............being spun just enough is usually best for long range accuracy. </div></div>
That's the most relevant statement in this thread. Just ask the Benchrest match shooters about twist rates.
/shaking my head at the comments about barrel lengths and "overstabilization"....
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hamilton</div><div class="ubbcode-body">............being spun just enough is usually best for long range accuracy. </div></div>
That's the most relevant statement in this thread. Just ask the Benchrest match shooters about twist rates.
/shaking my head at the comments about barrel lengths and "overstabilization"....
Re: Why a 7 twist AR?
<span style="color: #333300"><span style="font-weight: bold">Why deal with all the confusion...
For LONG DISTANCE out of an AR15 platform, I would suggest just opting for an upper chambered in 6.5 Grendel!</span></span>
<span style="color: #333300"><span style="font-weight: bold">Why deal with all the confusion...
For LONG DISTANCE out of an AR15 platform, I would suggest just opting for an upper chambered in 6.5 Grendel!</span></span>
Re: Why a 7 twist AR?
6mm turbo improved is about as much as one could cram into the little AR (as of now).
30 AR necked down to 6mm may give it a run eventually.
http://www.6mmar.com/6mmAR_Turbo_40_Improved.php
One could show up at the 1000 yard line with a 16" barreled AR15 carbine (chambered in 6mm AR..........) And, in the right hands, stand a chance of out-shooting some folks.
I'd love to watch that unfold.
6mm turbo improved is about as much as one could cram into the little AR (as of now).
30 AR necked down to 6mm may give it a run eventually.
http://www.6mmar.com/6mmAR_Turbo_40_Improved.php
One could show up at the 1000 yard line with a 16" barreled AR15 carbine (chambered in 6mm AR..........) And, in the right hands, stand a chance of out-shooting some folks.
I'd love to watch that unfold.
Re: Why a 7 twist AR?
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Why deal with all the confusion...
For LONG DISTANCE out of an AR15 platform, I would suggest just opting for an upper chambered in 6.5 Grendel!</div></div>
Because if you are shooting service rifle in HP across the course & 1000 yard matches you are limited to the 223/5.56 in ARs.
This little table tells it all. Go with the 1:7 and you can shoot dern near anything from 52 - 90 grns.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Why deal with all the confusion...
For LONG DISTANCE out of an AR15 platform, I would suggest just opting for an upper chambered in 6.5 Grendel!</div></div>
Because if you are shooting service rifle in HP across the course & 1000 yard matches you are limited to the 223/5.56 in ARs.
This little table tells it all. Go with the 1:7 and you can shoot dern near anything from 52 - 90 grns.
Re: Why a 7 twist AR?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hamilton</div><div class="ubbcode-body">
6mm turbo improved is about as much as one could cram into the little AR (as of now).
30 AR necked down to 6mm may give it a run eventually.
http://www.6mmar.com/6mmAR_Turbo_40_Improved.php
One could show up at the 1000 yard line with a 16" barreled AR15 carbine (chambered in 6mm AR..........) And, in the right hands, stand a chance of out-shooting some folks.
I'd love to watch that unfold.</div></div>
Actually, the BRX is the hottest thing right now. Although, when you start seeing 30 AR's necked down to calibers with higher BC bullets that you can fit in the case and still feed from a magazine.
FWIW, the most power you can get from an AR platform is the WSSM's. But, they are too long to fit high BC bullets into.
Also, as KraigWY noted, there are a LOT of competitions that you <span style="text-decoration: underline">cannot</span> shoot anything but .308/7.62 or 5.56/.223
Another point here as well. As much as I like wildcats and maximizing potential of a round or a platform, there is something to be said about making <span style="font-style: italic">The single most common round in the world</span> your 'go-to' rifle. There will be an abundance of ammunition in many places if you need it.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hamilton</div><div class="ubbcode-body">
6mm turbo improved is about as much as one could cram into the little AR (as of now).
30 AR necked down to 6mm may give it a run eventually.
http://www.6mmar.com/6mmAR_Turbo_40_Improved.php
One could show up at the 1000 yard line with a 16" barreled AR15 carbine (chambered in 6mm AR..........) And, in the right hands, stand a chance of out-shooting some folks.
I'd love to watch that unfold.</div></div>
Actually, the BRX is the hottest thing right now. Although, when you start seeing 30 AR's necked down to calibers with higher BC bullets that you can fit in the case and still feed from a magazine.
FWIW, the most power you can get from an AR platform is the WSSM's. But, they are too long to fit high BC bullets into.
Also, as KraigWY noted, there are a LOT of competitions that you <span style="text-decoration: underline">cannot</span> shoot anything but .308/7.62 or 5.56/.223
Another point here as well. As much as I like wildcats and maximizing potential of a round or a platform, there is something to be said about making <span style="font-style: italic">The single most common round in the world</span> your 'go-to' rifle. There will be an abundance of ammunition in many places if you need it.
Re: Why a 7 twist AR?
I have much love, and respect, for the 223 and 308.
Palma now allows either.
At 1000 yards, I'd put my money on a good Palma shooter with an iron sighted 308 or 223 over any FNG with a scoped any-caliber.
Both calibers continue to impress me with what they are capable of.
I've witnessed some amazing, yet repeatable feats with either.
I have much love, and respect, for the 223 and 308.
Palma now allows either.
At 1000 yards, I'd put my money on a good Palma shooter with an iron sighted 308 or 223 over any FNG with a scoped any-caliber.
Both calibers continue to impress me with what they are capable of.
I've witnessed some amazing, yet repeatable feats with either.
Re: Why a 7 twist AR?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hamilton</div><div class="ubbcode-body">I have much love, and respect, for the 223 and 308.
Palma now allows either.
At 1000 yards, I'd put my money on a good Palma shooter with an iron sighted 308 or 223 over any FNG with a scoped any-caliber.
Both calibers continue to impress me with what they are capable of.
I've witnessed some amazing, yet repeatable feats with either.</div></div>
I would agree with that statement regarding an FNG. I certainly wouldn't agree if you are up against someone with equal experience as your Palma shooter behind a scope.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hamilton</div><div class="ubbcode-body">I have much love, and respect, for the 223 and 308.
Palma now allows either.
At 1000 yards, I'd put my money on a good Palma shooter with an iron sighted 308 or 223 over any FNG with a scoped any-caliber.
Both calibers continue to impress me with what they are capable of.
I've witnessed some amazing, yet repeatable feats with either.</div></div>
I would agree with that statement regarding an FNG. I certainly wouldn't agree if you are up against someone with equal experience as your Palma shooter behind a scope.
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