Twist Rate

[bench]

Does over twist reduce how accurate a bullet can be,such as bullet that requires a 12 twist but your barrel is 9 or 10 twist.
How much does over twist affect the bullet other than a bullet coming apart in flight.

 

[Joe Salt]

Are you talking 30 Cal. Some people get upset if you use the wrong Definition or spell words wrong! ;D

Joe Salt

 

[bench]

Not sure how to take your reply!!
22 Cal

 

[JRS]

Which bullet weights bench?

 

[bench]

I like to shoot Berger Varmint but also Cutting Edge Bullets and the non lead bullets require more twist.
40gr on the low side and 55gr will be the high side

 

[bench]

gstaylorg,
Thanks for the info.

 

[DennisH]

My 223 has a 9 twist and will shoot anything. It shoots 52 grain flat base the best.

My 308 is a 10 twist and will shoot anything sub MOA. From 110 grain to 190's

Now the rest of my rifles are a little more picky.

Dennis

 

[r bose]

Bullet manufacturers give twist rates needed to stabilize a particular bullet they manufacture. I think it would be hard to over twist any 224 cal bullet in a 9, 8, or even a 7 twist barrel.

Most 223 shooters try to do just the opposite. They want to shoot heavy bullets (70-90g) in to slow a barrel and that's where problems start.

 

[CatShooter]

Bullet manufacturers give twist rates needed to stabilize a particular bullet they manufacture. I think it would be hard to over twist any 224 cal bullet in a 9, 8, or even a 7 twist barrel.

Most 223 shooters try to do just the opposite. They want to shoot heavy bullets (70-90g) in to slow a barrel and that's where problems start.

It is soooooooo easy to over spin the .224 calibre Sierra Blitz and the Hornady SX bullets - I have watch hundreds of them fly apart before they hit the 100 target.

 

[dedogs]

Not a mathematician, but doesn't velocity also factor in? In other words if you slow down your velocity in a fast twist barrel does that help in keeping the bullet from vaporizing?

 

[CatShooter]

Not a mathematician, but doesn't velocity also factor in? In other words if you slow down your velocity in a fast twist barrel does that help in keeping the bullet from vaporizing?

Yup... but that kinda defeats the purpose...

 

[dedogs]

LOL You have a good point.

 

['Freak]

Cipherin’ projectile RPM is easy enough if you know the muzzle velocity and twist rate. Assuming here 3500 fps at the muzzle from a 1 in 10 twist:

3500 * (12/10) * 60 = 252,000 projectile rpm

Or, same mess only dumbed down a bit:

3500 * 720 / 10 = 252,000 rpm

Finding or begging a maximum rpm figure from the bullet manufacturer may not be so easy.

 

[lpreddick]

i have spun apart many a .224 varmint bullet when spinning too fast. 60 and 64 bergers don't like my 8 tw 22 BR but thrive in my 12 tw 22 BR. my understanding of bullets poofing at 75 yds is that the core melts and renders the bullet very unstable and the thin jacket being very hot ...comes apart. i am under the impression that a fast twist will magnify any internal flaws a bullet may have, resulting in poofs or a flyer. i may be wrong on this one but i wonder if each bullet has an optimum RPMS for it's perfect flight, whether you achieve these RPMS by twist or speed.

 

[CatShooter]

i have spun apart many a .224 varmint bullet when spinning too fast. 60 and 64 bergers don't like my 8 tw 22 BR but thrive in my 12 tw 22 BR. my understanding of bullets poofing at 75 yds is that the core melts and renders the bullet very unstable and the thin jacket being very hot ...comes apart. i am under the impression that a fast twist will magnify any internal flaws a bullet may have, resulting in poofs or a flyer. i may be wrong on this one but i wonder if each bullet has an optimum RPMS for it's perfect flight, whether you achieve these RPMS by twist or speed.

The core does not melt - the spinning force rips the jacket along the rifling cuts and the jacket fails... which is why when Berger had problems with their long range match bullets going poof, they went to a thicker jacket.

Little heat is actually conducted to the bullet in the ~1.5 thousandths of a second it travels down the bore.

 

[barefooter56]

All,
Bryan Litz,s book "Modern Advancements In Long Range Shooting pretty much covers this in chapter 1 "Twist Rate and muzzle velocity" good read. We have thickened the jackets slightly on our target bullets to insulate the lead core to resist bullet failure on the way to the target. Some feedback from shooters also indicate that the type of rifling and amount of wear on the bore can impact bullet failure also. One of the techs here was having issues with bullets exploding in a .22-250 with a new cut rifles barrel. He tried a 5R barrel (new) with the same load and the problem ended. Same thing has been indicated by shooters who had the bullet failure issue but noticed that it was reduced or eliminated as the barrel got more rounds on it. Your results may vary.

 

['Freak]

It’s centrifugal force from overly high RPM acting on the bullet’s innards and overcoming the jacket’s ability to hold the mess in, so “poof”. There’s no poof until the projectile exits the barrel leaving only the jacket, by now damaged goods, to constrain the rotating mass all by its lonesome.

 

[CatShooter]

It’s centrifugal force from overly high RPM acting on the bullet’s innards and overcoming the jacket’s ability to hold the mess in, so “poof”. There’s no poof until the projectile exits the barrel leaving only the jacket, by now damaged goods, to constrain the rotating mass all by its lonesome.

Ha ha ha ha ha...

Well put!

 

[amamnn]

In ye olden days when I was first introduced to this subject, I was told that spinning the bullet faster than neccessary to stabilize it allowed more rotations of the bulllet on the way to the target and hence more opportunity for any flaw that causes the bullet to be out of balance to affect the path of the bullet on its way to the target, thus affecting accuracy and group size.

 

[barefooter56]

ole freak, Cat Shooter, amamnn,
Check out the chapter 1 in Bryan's MODERN ADVANCEMENTS IN LONG RANGE SHOOTING for more information and another view on why bullets may fail and the effects of a faster twist rate than needed. Kind of cleared up why my 1-9" twist Savage shot a 40 grain bullet so well. Just a suggestion.