Twist Rate - 300 Norma

[goosendmax]

For those of you that have experience with a 300 Norma Magnum what twist rates are you running and what bullets?
I’m really wanting to use the 245 Berger’s or the 250 A-Tips. Barrel length will be somewhere around 27-28” finished and was thinking of a twist rate of 1-7.5” to 1-8.5”.
Berger’s twist rate calculator says I’ll be way good with the 1-8.5”. Just curious to see everyone’s experience and thoughts.
Also, if I went with the 1-7.5” could I potentially over stabilize the bullet?
Thanks

 

[MrRedFox13]

Those are Questions I have also. Lol

 

[Evlshnngns]

250 Atip calls for 8.5 twist, I wouldn't go faster. I plan on getting a 9 twist, which works for the 245.

 

[Hawk in WY]

My 28 inch barrel is eight twist for the Barnes 212 bore rider.

It's hammer on elk.

 

[6AYoteHunter]

I am having a 8.75 twist 28" built for berger 230 and 245.

 

[Frank Green]

I haven't tried anything heavier than the 230Atips, 230SMK and 225 ELDM's and my twist is 1-9. My gun is in 300PRC and I'm running them at 2900fps.

If you want to shoot the 250's then 1-8.5 min.

I would refrain from going 1-7.5 twist if you don't have to. If you are pushing the bullets 2800fps (just picking a number right now and that's probably on the high side with a 250) and a 7.5 twist.....that's spinning the bullet at 268,800rpm. Upper 200's and my hard line is 300k rpm and bullets are going to start coming apart. Also any runout your ammo has or any defects in the bullet and the faster twist will amplify these problems and cause accuracy issues.

If I was going to strictly run the heavies like the 250's....I wouldn't go faster than a 1-8. The 7.5 isn't going to give you anything extra.

Copper solid bullets get longer for length per given weight vs a lead core bullet. Length dictates twist needed more than the bullet weight most of the time.

Later, Frank
Bartlein Barrels

 

[goosendmax]

I haven't tried anything heavier than the 230Atips, 230SMK and 225 ELDM's and my twist is 1-9. My gun is in 300PRC and I'm running them at 2900fps.

If you want to shoot the 250's then 1-8.5 min.

I would refrain from going 1-7.5 twist if you don't have to. If you are pushing the bullets 2800fps (just picking a number right now and that's probably on the high side with a 250) and a 7.5 twist.....that's spinning the bullet at 268,800rpm. Upper 200's and my hard line is 300k rpm and bullets are going to start coming apart. Also any runout your ammo has or any defects in the bullet and the faster twist will amplify these problems and cause accuracy issues.

If I was going to strictly run the heavies like the 250's....I wouldn't go faster than a 1-8. The 7.5 isn't going to give you anything extra.

Copper solid bullets get longer for length per given weight vs a lead core bullet. Length dictates twist needed more than the bullet weight most of the time.

Later, Frank
Bartlein Barrels

Frank,
Thank you for the detailed reply. Exactly what is was looking for.

 

[Lowlight]

10....

10 works, 230gr Bergers at 2960fps out of a 25" barrel at 100 and it's even better at 2000

The 8 was a huge fuck up because the originator of that model was using a short barrel, if you want velocity, don't go quick on the twist it won't work

That is why everyone is being quiet again on the Norma, they ruined it with all the 8 twist talk

10 for jacketed and 9 for solids, no more ...

 

[shoot4fun]

My 300NM is an improved version and has a 9 twist Krieger on it.
I'll likely never shoot heavier than the 230 Berger or A-Tip in it.
Been shooting the Berger 230 OTM Hybrid out of a 10 twist 300WM for quite a while now and they shoot perfectly fine out to the 1,300 yards I've tried them.

 

[Lowlight]

9 is fine,

it's the 8s and less that are the biggest problem especially when guys push the velocity.

99% know they want to shoot far so they try to squeeze every ounce of MV out of the rifle, in doing so the faster twist cause a problem.

if you were shooting factory gun, factory ammo velocities it would probably be okay for 98% of them, even with an 8 twist, but once they start pushing velocities it gets very inconsistent.

 

[kthomas]

I have 1:8 twist barrels, in my limited testing haven't seen an issue yet, but I also encounter pressure much earlier then other people do. I'm pushing 230 Bergers at 2950 fps out of a ~29" barrel. If I go much faster then that, I encounter pressure. I'm not sure if that's due to the faster twist, the small(ish) lugs of the Defiance action, and/or other factors that's making that happen. But perhaps my slow(ish) speeds are allowing me to avoid trouble with the faster twist.

Knowing what I know now with what others are experiencing, I would get future barrels in at least 1:9 twist. There's nothing to really gain from a 1:8 twist, and there's definitely potential issues with the fast twist and jacketed bullets. I have two barrels in 1:8 twist to burn out before then, but since moving to AZ I haven't found any good local spots near me to stretch out the .300NM, so it's mostly been neglected to this point.

In the future I may do what @lowlight is doing, using a shorter (~26") barrel with a 1:10 or 1:9 twist. May even do a .300NM Improved.

 

[Hawk in WY]

Over spinning the bullet can definitely lead to problems. Solid copper is probably the exception. I went 8 twist on a 28-inch barrel because that is the minimum Barnes recommends for their 212 gr bore rider all copper bullet. I suspect the reason an 8 twists works as well as it does is that the solid bullet is not going to come apart and the heavier copper bullet is longer.

 

[shoot4fun]

I have 1:8 twist barrels, in my limited testing haven't seen an issue yet, but I also encounter pressure much earlier then other people do. I'm pushing 230 Bergers at 2950 fps out of a ~29" barrel. If I go much faster then that, I encounter pressure. I'm not sure if that's due to the faster twist, the small(ish) lugs of the Defiance action, and/or other factors that's making that happen. But perhaps my slow(ish) speeds are allowing me to avoid trouble with the faster twist.

Knowing what I know now with what others are experiencing, I would get future barrels in at least 1:9 twist. There's nothing to really gain from a 1:8 twist, and there's definitely potential issues with the fast twist and jacketed bullets. I have two barrels in 1:8 twist to burn out before then, but since moving to AZ I haven't found any good local spots near me to stretch out the .300NM, so it's mostly been neglected to this point.

In the future I may do what @lowlight is doing, using a shorter (~26") barrel with a 1:10 or 1:9 twist. May even do a .300NM Improved.

I can only relate my comparison of two rifles chambered in .223 with Krieger barrels of different twist rate. I have one 7.7 twist and shooting 80 Berger VLD with Varget at 2,980 FPS. Thinking I could get improvement on drop and drift with the 90 VLD, I chambered a same length barrel of 6.5 twist. I believe it was a mistake. The 6.5 twist hits pressure, I believe, way sooner than I thought it should/would. I lose roughly 200 FPS from one rifle to the other and, best I have determined, I am either no better off (maybe worse) shooting 90's versus 80's.
Plus, although I haven't tried it, I feel I would have to deal with lighter bullets coming apart in that fast a twist if I tried the 80 in it.

 

[MrRedFox13]

I have 1:8 twist barrels, in my limited testing haven't seen an issue yet, but I also encounter pressure much earlier then other people do. I'm pushing 230 Bergers at 2950 fps out of a ~29" barrel. If I go much faster then that, I encounter pressure. I'm not sure if that's due to the faster twist, the small(ish) lugs of the Defiance action, and/or other factors that's making that happen. But perhaps my slow(ish) speeds are allowing me to avoid trouble with the faster twist.

Knowing what I know now with what others are experiencing, I would get future barrels in at least 1:9 twist. There's nothing to really gain from a 1:8 twist, and there's definitely potential issues with the fast twist and jacketed bullets. I have two barrels in 1:8 twist to burn out before then, but since moving to AZ I haven't found any good local spots near me to stretch out the .300NM, so it's mostly been neglected to this point.

In the future I may do what @lowlight is doing, using a shorter (~26") barrel with a 1:10 or 1:9 twist. May even do a .300NM Improved.

2950 on a 230 is pretty fast imo. *however I'd like to be able to run mine at 3k lol* what is fast in your opinion?

 

[Geno C.]

2950 on a 230 is pretty fast imo. *however I'd like to be able to run mine at 3k lol* what is fast in your opinion?

@CompMatch91

 

[kthomas]

2950 on a 230 is pretty fast imo. *however I'd like to be able to run mine at 3k lol* what is fast in your opinion?

It seems that there are a fair number of people getting 3000-3100+ fps with 28+ barrels. In this thread alone there's an example, with Frank getting 2950 fps (same speed) with a barrel that's 4" shorter.

 

[MrRedFox13]

It seems that there are a fair number of people getting 3000-3100+ fps with 28+ barrels. In this thread alone there's an example, with Frank getting 2950 fps (same speed) with a barrel that's 4" shorter.

Is that a .300 norma also or a .300-378 for Frank's rifle lol

 

[Lowlight]

I had a load that was 2990fps too heavy a bolt lift ... the rifle was not Able to handle it

I recently switched my Legacy AWSM to a dedicated 300NM and it can handle the pressures much better

 

[goosendmax]

10....

10 works, 230gr Bergers at 2960fps out of a 25" barrel at 100 and it's even better at 2000

View attachment 7594492

The 8 was a huge fuck up because the originator of that model was using a short barrel, if you want velocity, don't go quick on the twist it won't work

That is why everyone is being quiet again on the Norma, they ruined it with all the 8 twist talk

10 for jacketed and 9 for solids, no more ...

lowlight,
Thank you for the much needed information. Here’s the problem I’m running into. I have everything I need right now to build this rifle, and the option between two barrels. One is a 1:8.5” twist and the other is a 1:10” twist. I originally was only going to run Berger 230’s but have since changed my mind and really want to go with the Berger 245’s and the Hornady 250’s and was leaning towards the 1:8.5” barrel with a finish length of 28”.
What I understand after reading your post is I would be better off going with the 1:10” twist barrel because I will be able to obtain faster velocities, experience less pressure, and still stabilize the longer heavy bullets just fine without worrying about jacket separation and still get excellent groups.
Whereas if I went with the 1:8.5” I’m going to have to run slower speeds to stay away from excessive pressures and could risk jacket separation and overall completely ruin my hopes and dreams for this rifle.
So, after all that being said, if I went with the 1:10” twist at 28” I could run any bullet from 200-250 grain and be very happy right?

 

[Lowlight]

Yes,

You want the 1-8.5 to run around 2800fps and the 1-10 can go higher based on my experience With the round

In my mind, the 1-8 works in replicating a 338LM, but the 1-10 makes the Norma what it is compared that cartridge

 

[CompMatch91]

For those of you that have experience with a 300 Norma Magnum what twist rates are you running and what bullets?
I’m really wanting to use the 245 Berger’s or the 250 A-Tips. Barrel length will be somewhere around 27-28” finished and was thinking of a twist rate of 1-7.5” to 1-8.5”.
Berger’s twist rate calculator says I’ll be way good with the 1-8.5”. Just curious to see everyone’s experience and thoughts.
Also, if I went with the 1-7.5” could I potentially over stabilize the bullet?
Thanks

Been running 1-8 for a year now and strictly sending 250’s out. Shoots hole for hole at 100, girlfriend just shot at Spearpoint for the first match Saturday and took 4th with it.

 

[CompMatch91]

2950 on a 230 is pretty fast imo. *however I'd like to be able to run mine at 3k lol* what is fast in your opinion?

That’s what I push 250’s at. No pressure.

 

[CompMatch91]

I had a load that was 2990fps too heavy a bolt lift ... the rifle was not Able to handle it

I recently switched my Legacy AWSM to a dedicated 300NM and it can handle the pressures much better

What brass?

 

[NoLegs24]

That is why everyone is being quiet again on the Norma, they ruined it with all the 8 twist talk

10 for jacketed and 9 for solids, no more ...

 

[Lowlight]

was using Norma brass and whatever was leftover

 

[CompMatch91]

View attachment 7594844

To the OP do whatever this guy does, I saw him shoot a 300nm in Wyoming last June.

 

[MrRedFox13]

That’s what I push 250’s at. No pressure.

That's even better

 

[CompMatch91]

was using Norma brass and whatever was leftover

I noticed pressure with Norma brass well before Lapua, from my understanding Peterson is by far the best.

 

[kthomas]

I noticed pressure with Norma brass well before Lapua, from my understanding Peterson is by far the best.

I've heard similar things.

I'm using Norma brass, so that makes sense. Perhaps when I wear the brass out I will go Peterson.

 

[Dead Eye Dick]

I did a lot of work with a .221 Fireball using a 7 twist. Velocity is not that high but pressure levels get critical REAL QUICK. Between not enough pressure to stabilize the case in the chamber and over pressure signs with sticky extraction and heavily flattened/cratered primers was caused by a 0.3 grain difference pushing a 80 grain Berger. Hit the sweet spot and that little round can do big things momentum wise. However, that tiny round, trying to push heavy bullets down a fast twist barrel is real hard on the gun, hence the critical powder charge weights. It actually was able to send a 90 grain Sierra. In testing, a slight wobble was seen on paper at 50 meters but the group at 200 meters was still within limits to reliably take down rams. Still, why push the firearm any harder when the 80 grains will do the job.

I suppose the point here is, there is no free lunch. Faster and faster twists can stabilize very long bullets but pressure rise and bullet fraiilability both come into play. What is marginal may not actually be marginal at all. The 9 twist in a .223 is not supposed to be able to stabilize a 77 grain Sierra but in a Savage Striker, pushing the bullet quite hard, proved very successful.

 

[shoot4fun]

The 9 twist in a .223 is not supposed to be able to stabilize a 77 grain Sierra but in a Savage Striker, pushing the bullet quite hard, proved very successful.

While we have been led to believe the 77SMK required a minimum of 8 twist for stabilization, I was told not that long ago by a Sierra tech that the 77SMK was actually designed with nine twist in mind. That bullet worked extremely well in my 9 twist 22-250 barrel.

 

[wildcats]

My last 2 300 norma mags have been 9 twist,and the next one will be 9 as well,only a 35 shoulder

 

[shoot4fun]

My last 2 300 norma mags have been 9 twist,and the next one will be 9 as well,only a 35 shoulder

Mine is a 35˚ shoulder. Still in process of forming brass from factory Berger ammo. It is a project that has, unfortunately, been on the to-do list for too long.

 

[Frank Green]

I have 1:8 twist barrels, in my limited testing haven't seen an issue yet, but I also encounter pressure much earlier then other people do. I'm pushing 230 Bergers at 2950 fps out of a ~29" barrel. If I go much faster then that, I encounter pressure. I'm not sure if that's due to the faster twist, the small(ish) lugs of the Defiance action, and/or other factors that's making that happen. But perhaps my slow(ish) speeds are allowing me to avoid trouble with the faster twist.

Knowing what I know now with what others are experiencing, I would get future barrels in at least 1:9 twist. There's nothing to really gain from a 1:8 twist, and there's definitely potential issues with the fast twist and jacketed bullets. I have two barrels in 1:8 twist to burn out before then, but since moving to AZ I haven't found any good local spots near me to stretch out the .300NM, so it's mostly been neglected to this point.

In the future I may do what @lowlight is doing, using a shorter (~26") barrel with a 1:10 or 1:9 twist. May even do a .300NM Improved.

Twist for the most part has nothing to do with and or effect pressure. I've got way to much data from ammunition pressure test barrels that proves that. 10 vs 8 twist vs 12 twist etc...

Also any real world difference your see in velocity is minimal and usually comes down to the individuality of each barrel. Bore and groove size dimensions from one barrel to the next is the main one assuming the same chamber reamer was being used.

I agree though like I posted no need to go to a 1-7.5 or even a 8 twist. I don't see it giving you anything extra.

Later, Frank
Bartlein Barrels

 

[Frank Green]

Over spinning the bullet can definitely lead to problems. Solid copper is probably the exception. I went 8 twist on a 28-inch barrel because that is the minimum Barnes recommends for their 212 gr bore rider all copper bullet. I suspect the reason an 8 twists works as well as it does is that the solid bullet is not going to come apart and the heavier copper bullet is longer.

The solids like I stated given an equal weight as a lead core type bullet....the solids usually end up getting longer in length. Length dictates twist more than the actual weight does. Yes other things like velocity etc...play a small part as well.

Over spinning a solid bullet just like a lead core bullet.....creates problems as well. So people think spinning it faster will help the bullet if it has balance and or design issues....Ummm....I say no. Spinning it faster solid or not...usually amplifies the problem with the bullet.

 

[Geno C.]

The solids like I stated given an equal weight as a lead core type bullet....the solids usually end up getting longer in length. Length dictates twist more than the actual weight does. Yes other things like velocity etc...play a small part as well.

Over spinning a solid bullet just like a lead core bullet.....creates problems as well. So people think spinning it faster will help the bullet if it has balance and or design issues....Ummm....I say no. Spinning it faster solid or not...usually amplifies the problem with the bullet.

Enough to make the transition to subsonic is all I try and use

 

[THEIS]

Hi,

ModBB Left hand gain twist exiting at a 7.....
At time of pictures the T&E rifle had less than 40 rounds through it.

Then first round impact on 1 MOA target at 1k after stepping to 600 and 800 IIRC.

7 out of 10 at 1 Mile...24x24 target.

Sincerely,
Theis

 

[Frank Green]

Hi,

ModBB Left hand gain twist exiting at a 7.....
At time of pictures the T&E rifle had less than 40 rounds through it.

View attachment 7595136

Then first round impact on 1 MOA target at 1k after stepping to 600 and 800 IIRC.
View attachment 7595139

7 out of 10 at 1 Mile...24x24 target.
View attachment 7595142


Sincerely,
Theis

Hey Theis! I was wondering if you got around to shooting any of those sticks yet? Looks like they're working for ya!

Later, Frank

 

[Hawk in WY]

The solids like I stated given an equal weight as a lead core type bullet....the solids usually end up getting longer in length. Length dictates twist more than the actual weight does. Yes other things like velocity etc...play a small part as well.

Over spinning a solid bullet just like a lead core bullet.....creates problems as well. So people think spinning it faster will help the bullet if it has balance and or design issues....Ummm....I say no. Spinning it faster solid or not...usually amplifies the problem with the bullet.

Agreed.

My decision to go eight twist was driven by Barnes' recommendation of an eight twist for their 212 gr bore rider.

I have barrels with both eight (28 inch) and nine twist (26 inch). I suspect either will work with the 212 bore rider, but it will be an interesting experiment.

 

[brianf]

several questions about twist rate and muzzle velocity,

ive seen bits and pieces of this information all over the hide but at times its confusing as usual lol

any info and insight is greatly appreciated

twist and effect on pressure: @Frank Green
"Twist for the most part has nothing to do with and or effect pressure"
From what ive read gain twists are said to reduce initial bullet torque (less deformation) and reduce pressure...


bullet stabilization- twist and velocity:
Greenhill and Miller stability factor is muzzle velocity and twist rate
common knowledge is a quality jacketed bullet should not exceed 300,000 RPM because it might come apart in flight
yet bullets need 250,000+ RPM (depending) to get them stabilized

in theory if RPM is really a factor of velocity and twist rate, you should be able to get the same stability factor in a 1 in 20 twist barrel as a 1 in 10 twist barrel if you 2x the velocity

2x the velocity will give you the same RPM (removing all the pressure issues etc)

what am i missing?

thanks
brian

 

[THEIS]

Hi,

Greenhill formula​

T=150 x D
_____
R

T is the twist required (number of inches for one revolution),
D is the bullet diameter (in inches)
R is the bullet length to diameter ratio, (length divided by diameter)

Stability factor​

Solving Miller's formula for {\displaystyle s}

gives the stability factor for a known bullet and twist rate:

{\displaystyle {s}={\frac {30m}{t^{2}d^{3}l(1+l^{2})}}}

Twist in inches per turn​

Solving the formula for {\displaystyle T}

gives the twist rate in inches per turn:

{\displaystyle {T}={\sqrt {\frac {30m}{sd^{3}l(1+l^{2})}}}}

Sincerely,
Theis

 

[shoot4fun]

Hi,

Greenhill formula​

T=150 x D
_____
R

T is the twist required (number of inches for one revolution),
D is the bullet diameter (in inches)
R is the bullet length to diameter ratio, (length divided by diameter)

Stability factor​

Solving Miller's formula for {\displaystyle s}

gives the stability factor for a known bullet and twist rate:

{\displaystyle {s}={\frac {30m}{t^{2}d^{3}l(1+l^{2})}}}

Twist in inches per turn​

Solving the formula for {\displaystyle T}

gives the twist rate in inches per turn:

{\displaystyle {T}={\sqrt {\frac {30m}{sd^{3}l(1+l^{2})}}}}

Sincerely,
Theis

So, which one is the most correct?

 

[THEIS]

So, which one is the most correct?

Hi,

Depends on if you throw darts right handed or left handed

I over-stabilize according to both systems so never really payed attention to either of them, lololol

Sincerely,
Theis

 

[Lowlight]

I think Patagonia's stabilizer using both methods is best, the way Gus let's you visualize the impact of the twist is pretty good.

the problem with overstabliziing you are dependent on the weakest link in our system. you are tied to the quality of the bullet which was mass produced and can come apart.

 

[shoot4fun]

Hi,

Depends on if you throw darts right handed or left handed

I over-stabilize according to both systems so never really payed attention to either of them, lololol

Sincerely,
Theis

Using Berger's Twist Rate Stability Calculator the end result is displayed as SG. There are three "zones" to include Unstable, Marginal Stablity and Comfortable Stability. Manipulating the input values of the 215 Hybrid to 3,200 FPS with a 7 twist barrel one would think that it would be ideal, in fact, because the program tells me my bullet will be flying with full stability and I should except excellent groups based on an SG of 2.83. There is never any warning that such a situation could produce blown up bullets.
Misleading or misunderstood?

 

[Frank Green]

several questions about twist rate and muzzle velocity,

ive seen bits and pieces of this information all over the hide but at times its confusing as usual lol

any info and insight is greatly appreciated

twist and effect on pressure: @Frank Green
"Twist for the most part has nothing to do with and or effect pressure"
From what ive read gain twists are said to reduce initial bullet torque (less deformation) and reduce pressure...


bullet stabilization- twist and velocity:
Greenhill and Miller stability factor is muzzle velocity and twist rate
common knowledge is a quality jacketed bullet should not exceed 300,000 RPM because it might come apart in flight
yet bullets need 250,000+ RPM (depending) to get them stabilized

in theory if RPM is really a factor of velocity and twist rate, you should be able to get the same stability factor in a 1 in 20 twist barrel as a 1 in 10 twist barrel if you 2x the velocity

2x the velocity will give you the same RPM (removing all the pressure issues etc)

what am i missing?

thanks
brian

Brian, Velocity plays a part as does the environment/conditions/temperature you are shooting in. For example a guy shooting in Denver at 5000' elevation can usually get away with a twist that is on the edge of stabilizing the bullet or in fact even run a slightly slower twist and not have any problems but a guy who is shooting at or near sea level he's going to have issues.

Let's stick with 30 cal and a 175gr conventional jacketed match bullet. I've seen those bullets fly out of a true 13 twist barrel (I'd never run one myself though) but lets call that the minimum twist at that velocity to stabilize that bullet. So at 2600fps and lets use a 12 twist barrel the bullet is comes out at 156,000rpm.

Same info as above but now let's make it a 10 twist barrel....now the rpm is at 187,200rpm.

I've shot 12 twist, 11.25, 11, 10 twist and even 8 twist....and the 8 twist is spinning them at 234,000rpm even though it doesn't need it but all shoot fine.

Now let's run that same bullet out of a 300WM at 3100fps in a 12 twist they come out at 186,000rpm and the 10 twist is 223,200rpm and a 8 twist is 279,000rpm.

For giggles....at 1200fps and a 12 twist barrel the bullet comes out at 72,000rpm. If memory serves me correctly at that velocity of 1200fps which is just above speed of sound that bullet needs a 1-10.93 min twist. I've shot those bullets out of a 308w at 100 yards only at that velocity and in a 10 twist and the gun/ammo shot excellent groups. In a 10 twist barrel the bullet is spinning at 86,400 rpm. I didn't shoot it any further distance wise. Kind of what's the point....it's subsonic before it even gets to 200 yards for sure. So you can look at everything here and double the numbers how ever you want. The bullet is stable out of a 10 twist barrel at 1200fps and double the velocity the rpm pretty much doubles/goes up as well at 308w velocities.

The gain twist has not been proving by a given test method to reduce pressure. We did make test barrels that went from a 12 to a 8 twist both in 308w and 6.5CM but not thinking far enough ahead....we made a standard pressure test barrel that measures pressure on the chamber/case itself. Comparing the data to an identical test barrel in a straight 12 twist for a 308w and a 8 twist for the 6.5CM there was no measurable difference.

What needs to be done and with the current state of affairs with the gun industry I don't see the test happening is we have made a couple more barrels and put in an additional pressure test port. Chamber being one as it's standard....next one 6" down from the chamber. What we would need to see is if the pressure is dropping faster(I call it helping the spike) in front of the chamber. If this test can be run.....and it does show that....then we have something to show.

I've always been told and from what I've seen and will say it again....for the most part twist has nothing to do with the pressure. I have to go with what I know as of right now.

Yes there is a belief and to an extent I can agree with it that it can help with reducing deformation of the bullet as you called it.

So as this example shows you don't necessarily need 250k rpm to stabilize the bullet. Some calibers/bullets might need it but not all.

Later, Frank

 

[Frank Green]

I think Patagonia's stabilizer using both methods is best, the way Gus let's you visualize the impact of the twist is pretty good.

the problem with overstabliziing you are dependent on the weakest link in our system. you are tied to the quality of the bullet which was mass produced and can come apart.

View attachment 7595485

What he said!!!!!!!!

 

[phlegethon]

What he said!!!!!!!!

How accurate do you think the predictions are regarding reduced BC with marginal stability, for example when the Berger calculator says the effective BC is only 95% of the max?

 

[brianf]

Thanks f

Brian, Velocity plays a part as does the environment/conditions/temperature you are shooting in. For example a guy shooting in Denver at 5000' elevation can usually get away with a twist that is on the edge of stabilizing the bullet or in fact even run a slightly slower twist and not have any problems but a guy who is shooting at or near sea level.

Let's stick with 30 cal and a 175gr conventional jacketed match bullet. I've seen those bullets fly out of a true 13 twist barrel (I'd never run one myself though) but lets call that the minimum twist at that velocity to stabilize that bullet. So at 2600fps and lets use a 12 twist barrel the bullet is comes out at 156,000rpm.

Same info as above but now let's make it a 10 twist barrel....now the rpm is at 187,200rpm.

I've shot 12 twist, 11.25, 11, 10 twist and even 8 twist....and the 8 twist is spinning them at 234,000rpm even though it doesn't need it but all shoot fine.

Now let's run that same bullet out of a 300WM at 3100fps in a 12 twist they come out at 186,000rpm and the 10 twist is 223,200rpm and a 8 twist is 279,000rpm.

For giggles....at 1200fps and a 12 twist barrel the bullet comes out at 72,000rpm. If memory serves me correctly at that velocity of 1200fps which is just above speed of sound that bullet needs a 1-10.93 min twist. I've shot those bullets out of a 308w at 100 yards only at that velocity and in a 10 twist and the gun/ammo shot excellent groups. In a 10 twist barrel the bullet is spinning at 86,400 rpm. I didn't shoot it any further distance wise. Kind of what's the point....it's subsonic before it even gets to 200 yards for sure. So you can look at everything here and double the numbers how ever you want. The bullet is stable out of a 10 twist barrel at 1200fps and double the velocity the rpm pretty much doubles/goes up as well at 308w velocities.

The gain twist has not been proving by a given test method to reduce pressure. We did make test barrels that went from a 12 to a 8 twist both in 308w and 6.5CM but not thinking far enough ahead....we made a standard pressure test barrel that measures pressure on the chamber/case itself. Comparing the data to an identical test barrel in a straight 12 twist for a 308w and a 8 twist for the 6.5CM there was no measurable difference.

What needs to be done and with the current state of affairs with the gun industry I don't see the test happening is we have made a couple more barrels and put in an additional pressure test port. Chamber being one as it's standard....next one 6" down from the chamber. What we would need to see is if the pressure is dropping faster(I call it helping the spike) in front of the chamber. If this test can be run.....and it does show that....then we have something to show.

I've always been told and from what I've seen and will say it again....for the most part twist has nothing to do with the pressure. I have to go with what I know as of right now.

Yes there is a belief and to an extent I can agree with it that it can help with reducing deformation of the bullet as you called it.

So as this example shows you don't necessarily need 250k rpm to stabilize the bullet. Some calibers/bullets might need it but not all.

Later, Frank

Thanks for the thorough reply.

I’ll ponder and bother you again.

 

[MrRedFox13]

Got ya'll, buy a barrel. Run every bullet weight at 90% max load use what ever shoots best.