Twist Rate vs Velocity

[300meter]

Hypothetical question, given you have two 308 rifles, same barrel length, both shooting factory Federal 168gr Match Ammo. One rifle has a 1:12 twist barrel and the other a 1:14 twist, how much velocity difference would you expect to see based on the difference in twist rate?

 

[ar10ar15man]

never seen this as an issue...
might depend on the powder burn rate
technically the 1/12 twiist requires more work/energy than the 1/14.....

but with that small of a diff, the powder burn rate could offset the additional work....

you get what you pay for..my 2 cents worth

 

[ar10ar15man]

the problem is no two bbls are identical....
the work to move a bullet in the 1/14 twist might be more than in the 1/12 ..depends on the bbl
truely IDENTICAL less twist...see my first post....
AND YEP ITS GONNA BE SMALL

 

[M-61]

the problem is no two bbls are identical....
the work to move a bullet in the 1/14 twist might be more than in the 1/12 ..depends on the bbl
truely IDENTICAL less twist...see my first post....
AND YEP ITS GONNA BE SMALL

Wouldn't the energy level required be GREATER (NOT LESS) in a tighter twist? Therefore less energy in a 1-14 than a 1-12 and so on? All else being as equal as it can be.

I am looking for clarification on the above statement which I think says the opposite.

 

[Cold Bore]

As the rest are saying....

Theoroetically, yes, the 14-twist "should" shoot slightly faster.

However, differences in individual barrels, etc would make any difference too small to really matter.

If you are thinking ballistics, drop charts, etc, there is no substitute for actually shooting. What "should" happen, and theoreticals, only count for so much. The rest of reality is borne out on the range.

 

[M-61]

Though the difference is said to minuscule, I would like to know which is which, even though there may be no difference one can notice.

 

[mshelton]

From what I understand the slower twist rate allows you to run hotter loads with out getting what many refer to as 'spit' where one shot goes inexplicably out of the group, the twist however does not contribute to the velocity.

 

[Ackman]

One rifle has a 1:12 twist barrel and the other a 1:14 twist, how much velocity difference would you expect to see based on the difference in twist rate?

With a large difference......comparing a 14" twist to something with corkscrew-like twist of 7 or 8", you should see a very noticeable difference in velocity. "Theoretically" a barrel with only 2" slower twist should have a slight velocity advantage, but that doesn't mean it'll happen. Even two barrels with the same numbers can be real different. You never know, and there's no way to quantify this stuff. An example......years ago I had 2 guns barrelled by the same riflebuilder, same reamer and same headspace. Fired brass was interchangeable. These were .223's, one 14 twist button rifled Shilen, the other 12 twist H-S with cut rifling. Best load (50gr) for both guns was identical, with identical velocity and accuracy. It was just a fluke but it happened.

 

[armistemjim]

I have 308 match rifles with; 1x10, 1x12, 1x14 and the velocity difference is less than 50 fps with my cheap folding chrono. much the same results with friends lab unit. the difference is the distance i use these rifles at and bullet weight which as you know lighter equals faster. the one thing that will make a small difference is the finish and tightness of the bore. all hand lapped barrels are different in finish and bore dimension even if it is minuscule.

 

[searcher]

From differences I have chronographed from my rifles, I would "guess" around 75 F.P.S. if I were in a contest. Then again, I had two Krieger barrels bought at the same time, same twist, length, chamber reamer and chambered by the same gunsmith that shot the same load 100 f.p.s. apart. My summary would be to expect about as much difference in your barrel.