Barrel length vs twist rate

[Paddyd]

I'm all set to order my new barrel and have decided to stay with 308Win. My question is this. What is the heaviest bullets I can effectively stabilize in a 24", 11 twist barrel and not need to max out the charges? I do not shoot paper over 300 yards as that is all my local range allows for so I like to load more conservatively to both save cases as well as the throat. About the heaviest bullets I would ever shoot might be 175s, but 155 and 168s more the norm. Will 24 get it done or would 26 be better without having to pump up the velocity ?

 

[Orr89rocz]

If only that far, you’ll be fine with most anything with 24” and 11 twist. Berger vld up to 210 gr would fly. Berger twist calc would say marginally stable but thats fine for 300 yards

 

[Paddyd]

If only that far, you’ll be fine with most anything with 24” and 11 twist. Berger vld up to 210 gr would fly. Berger twist calc would say marginally stable but thats fine for 300 yards

Thanks.

 

[FeMan]

Increasing velocity does very little to increase stability. A few inches of barrel length will get you almost nothing in stability. A change in twist rate up or down will have a comparatively large effect.

Im not sure what your elevation is (that matters for twist rate and stability) but Id say a 1:12 or even slower would work. For optimal accuracy, a stability at 1.5 is best.

 

[RegionRat]

https://bergerbullets.com/twist-rate-calculator/

I agree with the others. At 300 yards or less, you don't need to worry at all till you get to really long or really heavy bullets. With the above link, you only need a little homework on a particular bullet to plug in the numbers and see what you get.

For example, at sea level, the Berger page spits out a table of recommended bullets for a 1:11 that go up to 185 Jugs.

 

[Rob01]

24" 11 twist will do you fine. I have a 20" 11 twist on one of my .308s and shoot it to over 1000 with 178s. I use 168 ELDs in my 26" 11 twist .308 for matches. Unless you are stepping into the 200+ range the 24" 11 will do just fine.

 

[Ned Ludd]

As has already been mentioned, within reasonable expected velocities from a given length barrel, the velocity has a much smaller effect than does the twist rate. Only when you reach the margins does velocity become more critical. For example, I ran the 200.20Xs at ~2650 fps from 30" 11"-twist barrels for years, and they shot just fine. Under the atmospheric conditions/elevations I shoot most often throughout the season, Berger's Twist Rate Calculator lists gyroscopic stability coefficients for those particular setups to be from ~1.35-1.39, which is sub-optimal. Nonetheless, I have won more than a few matches using that combination.

You can reasonably expect to run bullets up to ~185 gr (i.e. Juggernaut length bullets) out of a 12-twist barrel. They might be a little closer to the edge with the velocity you can expect from a 24" pipe, but they're not going to unexpectedly fall out of the sky or anything like that. Another consideration would be tipped bullets, such as Sierra's TMKs or Hornady offerings, as the ballistic tips may change the desired minimum twist rate for a bullet of a given weight class. I would be quite satisfied the 1:11 twist will effectively stabilize most, if not all, of the bullets in the weight range you listed.