223 Bullet Twist

[kraigWY]

You see a lot of post about bullet twist. Seems lots of people want to go to make do twist. Many dont agree with the Greenhill Fomula because it seems to call for a faster twist then one thinks he needs.

I disagree, I'm of the IF IN DOUBT, go faster crowd. Do you notice bullet makers and reloading manuals state for a given bullet, X TWIST OR FASTER.

Notice the "OR FASTER" part.

Anyway the Army did some test (listed in their M-16 Marskmanship Manual) that show the results of firing M193 (55 gr) and M 855 (62 gn) out of each, 1-12 twist M16A1, and 1-7 twist M16A2 at 500 yards. As you can see the 1-7 shoots both quite well, the 1-12 has problems with the heavier bullets.
The manual did indicate past 500 yards the heavier bullet does preform better in the faster twist.

 

[PistonPete]

Re: 223 Bullet Twist

is this post a question or a statement ?

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Seems lots of people want to go to make do twist.</div></div>

could you please clarify the above statement ?

 

[Austan]

Re: 223 Bullet Twist

It's a statement that people are "making due" with a less than ideal twist.

 

[ORD]

Re: 223 Bullet Twist

I agree with your premise Kraig, but I think that the statement applies almost exclusively to the civilian market and not to the military. In fact, most of the recent reports I have read suggest that the 1:7 twist barrel, like that referenced in the report you posted, is the ideal for the full compliment of ammunition offerings deployed by US Armed Forces.

There have been a lot of people recently trying to "squeeze" performance out of "tweaner" twist barrels (i.e. - people want to go to a 1:9 or 1:8 twist for everything under the sun and expect to increase performance which they aren't getting). Certainly, there are "optimum" barrel twists for a particular bullet at particular velocities with plenty of scientific data to back up the claims, however, for an "across the board" rifle, I will always urge people to go with faster than slower twist barrels.

 

[SIE107]

Re: 223 Bullet Twist

1 in 8 is fine.. anything slower than that.. your running into trouble.. the 1 in 6.5 bbl is like running into a wall.

 

[oneshot onekill]

Re: 223 Bullet Twist

I saw a video on (I think) Youtube of lightweight bullets actually exploding in mid-air as they exit the barrel of an AR with a "fast" twist. I'm still not sure it's real but WOW...

Just thought I'd throw that in here...

 

[AutoVerminator]

Re: 223 Bullet Twist

1/8 twist covers everything for an AR15 rifle that can be loaded to magazine length. (77gr smk and 75gr hpbt)

 

[scotharr]

Re: 223 Bullet Twist

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: AutoVerminator</div><div class="ubbcode-body">1/8 twist covers everything for an AR15 rifle that can be loaded to magazine length. (77gr smk and 75gr hpbt) </div></div>
Very true and a 1:8 can also handle a 75gr A-Max or 80gr SMK which are not mag-length. 90grainers would need a 1:7.

 

[Prairie Dog Dundee]

Re: 223 Bullet Twist

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: oneshot onekill</div><div class="ubbcode-body">I saw a video on (I think) Youtube of lightweight bullets actually exploding in mid-air as they exit the barrel of an AR with a "fast" twist. I'm still not sure it's real but WOW...

Just thought I'd throw that in here...</div></div>

Many of the thin skinned Varmint bullets will not hold up to even a one in nine twist. Years ago I was working up varmint loads for a Savage 110FP in 223 that has a one in nine twist rate. Hornady SX and Speer TNT bullets would not make fifty yards and would disapear in a little grey cloud of dust. The poly tip Nosler BT were fine. By the way, OP, the twist is not a bullet twist rather it is a barrel twist.

 

[Sterling Shooter]

Re: 223 Bullet Twist

My Service Rifles have been barreled and re-barreled with 1 in 7's for as long as I've been shooting in Service Rifle competition. I've shot 52's, 75's, 77 and 80 grain bullets with good results. The 52's are great for 100 yard reduced course shooting. The 77's work well at 200 and 300 yards. And, the 80's work well for 500, 600 and 1000 yard shooting.

What I don't understand is why shoot any bullet less than 50 grains from an AR in the first place. Even with a high MV, the light brick shaped bullets succumb to drag very quickly. With a 1 in 7 you can shoot 77's to insane distances for most any sort of target likely pursued with an AR. Hell, make 'em all 1/7.

 

[sotexhill]

Re: 223 Bullet Twist

You can even load the lighter bullets with the fast twist if you don't run them at a muzzle velocity which has them exiting the barrel at too high an RPM.

 

[Rovieairto]

Re: 223 Bullet Twist

A fact that is very often overlooked is that velocity matters greatly in this equation of stability.
Shorter barrels need faster twists.
I agree with Sterling Shooter and my service rifle went from a 1:8 to a 1:7 Kreiger (Not a 1:7.7).
With the 1:8, I had stability issues until I pushed the load to a higher pressure than I had originally wanted.
Once pushed hard, the load shot insanely well out of the 1:8.
There were lots of flyers until I got velocity up there though.
Seriously a half grain of powder made the load (80 grain A-max) shoot scores from the 170's to the 190's.
My 1:7 shoots just as well and there are no stability issues to worry about.

My 16" 1:8 twist Criterion is barely stabilizing Hornady's 75 HPBT.
0.5 grain will fix this but I wish it were a 1:7.

0.02

 

[Shooter21]

Re: 223 Bullet Twist

What kind of velocity should I be able to achive with a 1:7 twist tube measuring 26" and a 77 smk without punching it to a 223 AI?

 

[Rovieairto]

Re: 223 Bullet Twist

In the 2900's, at mag length, easy.

 

[Shooter21]

Re: 223 Bullet Twist

Sweet. I smell a new kreiger

 

[Barney88PDC]

Re: 223 Bullet Twist

I read that technically the bullet weight had nothing to do with the required twist. It was actually the amount of bearing surface that the bullet had. Longer surfaces need faster twist. Being just about all bullets as they get heavier get longer the statement "heavier bullets need a faster twist rate" is correct by default but again not actually dependant on weight.

Anyone can confirm or deny that?

 

[samnev]

Re: 223 Bullet Twist

I can't confirm but anecdotally my 52 grain HPBT sierra match has a longer oal than the 60 or 62 grain projos I shoot and is more accurate in my 1:7 twist rifles than either of the other 2.

 

[Rovieairto]

Re: 223 Bullet Twist

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Barney88PDC</div><div class="ubbcode-body">I read that technically the bullet weight had nothing to do with the required twist. It was actually the amount of bearing surface that the bullet had. Longer surfaces need faster twist. Being just about all bullets as they get heavier get longer the statement "heavier bullets need a faster twist rate" is correct by default but again not actually dependant on weight.

Anyone can confirm or deny that? </div></div>

It's actually the projectiles overall length that has the most effect on how much spin is required to stabilize.
The atmosphere that requires this stabilization is not effected by internal ballistics (I.E. Bearing surface will have zero effect).

When talking about specific bullets and twists, bullet velocity is just as important.
Example:
Under "normal" conditions a .224 80 grain A-max needs a 1-9 twist if shot at 22-250 velocities.
It needs a 1-8 if shot at high .223 velocities, and a 1-7 if shot at lower velocities, or at low density altitudes (cold air, low altitude).

It is misleading to say that the .224, 80 grain A-max requires "x" twist, without giving a velocity to go with it.

Velocity is just as important as twist rate.

 

[sotexhill]

Re: 223 Bullet Twist

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hamilton</div><div class="ubbcode-body"><snip>...When talking about specific bullets and twists, bullet velocity is just as important.
Example:
Under "normal" conditions a .224 80 grain A-max needs a 1-9 twist if shot at 22-250 velocities.
It needs a 1-8 if shot at high .223 velocities, and a 1-7 if shot at lower velocities, or at low density altitudes (cold air, low altitude).

It is misleading to say that the .224, 80 grain A-max requires "x" twist, without giving a velocity to go with it.

Velocity is just as important as twist rate.
</div></div>

I agree with what Hamilton said.

Velocity times twist rate determines the revolutions per minute (RPM) of the bullet as it exits the muzzle and goes downrange. Too high an RPM with a lightly constructed bullet and it can come apart. Too low an RPM and it may be unstable. Powder charge and barrel length affect muzzle velocity. So, saying a certain bullet requires a certain twist without specifying cartridge and, to a lesser extent, barrel length, doesn't tell the full story.