Barrel Twist in relation to Bullet Yaw

[PA PATRIOT]

I have done some reading on how a barrels twist rate can affect the yaw of a bullet after impact due to the bullet being under stabilized in flight. Now the one thing I cant find is how much of a affect a given twist rate may have on the popular 5.56 bullet weights from a standard 16" thur 20" barrel. Some say that a 1-12"inch twist is better for the 55gr to 62 grain bullets to cause earlier yaw while others claim a 1-14" twist. Now I understand there will be a affect on accuracy using these slower twist rates but if the engagement ranges were short less then 100yds what could one except? Would it still be CQC accurate.

[Zhukov]

The formula formula to determine the gyroscopic stability of a bullet is given by:



So an increase in w by going to a faster twist rate in the barrel is more than offset by the thousandfold increase in p once the bullet encounters tissue. In other words: Tissue is so much more dense than air that the slightly faster rate of bullet rotation is negligible; the bullet will be completely unstable as soon as it encounters tissue.

[PA PATRIOT]

I need a more "Layman's" reply if you would sir.

Thank you.
Phila PD

[Molon]

I need a more "Layman's" reply if you would sir.

Thank you.
Phila PD

As long as the bullet is adequately stabilized at the muzzle, barrel twist rate has no effect on the terminal ballistic properties of 5.56mm ammunition.

[butlers]

As long as the bullet is adequately stabilized at the muzzle, barrel twist rate has no effect on the terminal ballistic properties of 5.56mm ammunition.

I apologize for resurrecting this thread, but I'm researching a retro A1 build and I wanted to understand a bit more about the 1:12 twist rate (vs. the "modern" 1:7 twist rate).

From the information shared here, it seems that the following statement is wrong?

"This is important if you're shooting living targets, e.g., hunting because the fragments, combined with hydrostatic shock, tend to produce a much larger and more potentially lethal wound cavity than a bullet that stays in one piece. The relevance to rifling twist is that usually only a very rapidly spinning bullet - say, over 250,000 rpm - will fragment like that. A 1:12 twist won't produce that effect"
https://www.at3tactical.com/blogs/ne...rifling-part-2

So, 55gr XM193 out of a 14.5" barrel with 1:12 twist rifling goes around ~3000 fps and is spinning at 180,000 rpm according to this RPM calculator:
http://www.accurateshooter.com/techn...tes-stability/

Same bullet weight, same barrel length, but 1:7 twist rifling and slightly less velocity (~2900 fps) produces ~300,000 rpm.

The difference in RPM only effects the flight path of the bullet, and not the lethality -- right?

[T2C]

As long as the bullet is adequately stabilized at the muzzle, barrel twist rate has no effect on the terminal ballistic properties of 5.56mm ammunition.

I believe this statement sums up the affect twist rate has on terminal ballistics.

[Todd.K]

For practical understanding that statement still holds true. The simple answer is "barrier blind expanding" and then go train.

I have seen some discussions about higher RPM causing slightly more damage with some bullet designs, I believe fragmenting.

[rubber ducky]

Don't know how helpful this will be, but I've fired M855 through what i think it was a 1:14 (it could have been a 1:12) 16" bbl and it keyholed at 100m.

[tpe187]

As originally designed by Eugene Stoner, the M16 had a 1/14" twist. This kept the 55gr bullet at the ragged edge of stability. When the bullet impacted flesh it rapidly yawed and fragmented. In military testing by the Air Force in arctic conditions, it was determined that accuracy became unacceptable at 65 below and a change to 1/12 twist was recommended to further stabilize the round for arctic conditions - just in time for the jungles of Vietnam. "Misfire", pg 490.

Some critics contend that this single change resulted in the M16 being 40% less lethal with the change from 1/14 to 1/12 twist. "The Great Rifle Controversy" pg 199

The 1/7 twist of the M16A2 was in response to the length of the M856 tracer round, originally developed for the M249 SAW.

Unfortunately, most of the civilian examples of the AR15 use a 1/7 twist because that is what the military uses, though it is not the most appropriate twist.

[larry0071]

Ok, admitted dum-dum sticking his nose in here...... sorry....

Since I run basically 100 yards and less and only 55 gr XM193 ammo, would my 1:9 barrel be improved by being a 1:12 or 1:14? That is what I am hearing.

I don't ever plan to be shooting out past 100 yards because the property I shoot at does not readily provide me with that type of distance. I'm also not into the various military ammo types and I again buy what is readily available.... Federal XM193 black box or Wolf 55 grain .223 spec ammo.

It sounds as if the SHTF performance would be better with the 1:12 or 1:14 style twist, but that brings forth a new question... who makes a chrome lined, 16" or 14.5" carbine barrel with those slow twist rates?