On rifling twist...

[Slater]

In the Army's 1986 study on "Why The M16A2 Sucks And We Should Never, Ever Adopt It", one point was that the new 1 in 7 barrel twist was not what the Army was wanting. This was of course before 77 grain rounds and similar made their appearance. In their opinion, a 1:9 twist was optimal because:

"Reducing barrel twist to 1:9 will result in less stress on the bullet, barrel life will be improved, and barrel fouling will be reduced."

Not sure about the bullet stress and fouling issues, but in the 30+ years since the report came out, have there been any studies or research to validate or invalidate the Army's contention that a 1:9 twist would result in longer barrel life over a 1:7?

[Firefly]

Good question.

At one point 1:9 made sense, hence why a lot of Cold War 5.56 rifles were chambered in it.

Interesting topic sure

[Colt Carson]

I have read that faster twist results in shorter barrel life. Don’t remember where though.

[AndyLate]

The 62 grain M855 projectile works fine from a 1:9 twist.

I just picked up a 26" CZ bolt gun in .223 with 1:9 twist and I am looking forward to seeing how it shoots compared to my 18" barreled AR with 1:7 twist.

1:8 twist seems to be seen as a good compromise.

For what it's worth, 1:12, 1:9, 1:8, and 1:7 all seem to shoot the 55 grain bullets very well. The .223/5.56 just doesn't have the velocity to cause problems with light bullets and fast twist. A 22-250 or 220 Swift can drive a light bullet fast enough to come apart from rotational velocity/centrifugal force, though.

Andy

[vicious_cb]

Good question.

At one point 1:9 made sense, hence why a lot of Cold War 5.56 rifles were chambered in it.

Interesting topic sure

Not really, it's been tested to death. There really is no advantage to using a slower twist rates unless you want to shoot super light varmint loads out of longer barrels.



Personally I think we should so back to smooth bores and avoid this 1/7 vs 1/9 business. I mean it works for tanks right?

[Slater]

Not really, it's been tested to death. There really is no advantage to using a slower twist rates unless you want to shoot super light varmint loads out of longer barrels.



Personally I think we should so back to smooth bores and avoid this 1/7 vs 1/9 business. I mean it works for tanks right?

A fin-stabilized bullet - you may have something there

[jsbhike]

The 62 grain M855 projectile works fine from a 1:9 twist.

I just picked up a 26" CZ bolt gun in .223 with 1:9 twist and I am looking forward to seeing how it shoots compared to my 18" barreled AR with 1:7 twist.

1:8 twist seems to be seen as a good compromise.

For what it's worth, 1:12, 1:9, 1:8, and 1:7 all seem to shoot the 55 grain bullets very well. The .223/5.56 just doesn't have the velocity to cause problems with light bullets and fast twist. A 22-250 or 220 Swift can drive a light bullet fast enough to come apart from rotational velocity/centrifugal force, though.

Andy

An exception from what I have read (not personal expetience) is with Hornady SP SX bullets that allegedly will often come apart in .223 Remington with faster twists.

[markm]

The 62 grain M855 projectile works fine from a 1:9 twist.

Yep. But the M856 tracer is much longer, and might not be consistently stabile from rifle to rifle. I can't remember ever trying 856 in a 1/9 barrel, but the bullet is really long.

[vicious_cb]

An exception from what I have read (not personal expetience) is with Hornady SP SX bullets that allegedly will often come apart in .223 Remington with faster twists.

It also depends on jacket thickness. It not just about weight. Don't even get me started on those powder core varmint grenade bullets.

[Ned Christiansen]

The question of 1:7 twist being good or bad has been answered by time, to my satisfaction, other than the above-ref'd phenom of "dang, my 45-grainers are vaporizing half-way to that prairie dog", which I have personally experienced (and it's pretty hilarious).

I mean there are some theoretical downsides but to the best of my knowledge these are absorbed in the normal sphere of imperfection that exists in 5.56 ballistics and accuracy limitations.