Home Forums Hunting & Shooting Ask The Gunwriters Twist Calculator

Since asking the question about twist for a 30-06 barrel I've been looking at various bits of information. Here's a twist calculator posted by one of our Fire members on the Nosler Forum and shamelessly stolen by me. Plug in your numbers, hit enter and throw a beer bottle at the screen because you a may not agree with the answer. Like a .264 140 grain Accubond @ 2800 fps calls for a 1/9.4", not so bad. But a Long Range Accubond .308 dia 210 grain @ 2650 shows 1/11.0" ?????? And a .308 200 grain Accubond @ 2700 a 1/11.6". Then there's a 77 grain .224 Custom Competition that should be good at .......drum roll................1/9.7". Read 'em and weep.

Twist Calculator HERE

So for your 30-06 a 10" twist will handle it and give you some safety margin even in cold, dense air. What's the problem?

Another calculator:

HERE

I've used that one a few times.

No problem, just interesting. Never really researched twist before. Seems some opinions of high twist may be supported by the ability of current bullets to be spin proof on the up side. And the more spin imparted, the more spin while penetrating and a straighter line of penetration, maybe. I'm starting to see my concern about twist between 1/10 and 1/11 for bullets up to the 200gr Accubond is a flea fart of sorts. Actually ordered a 1/10.5" earlier today anyway. Figured it'd work and nobody else will have one.

Brilliant.

Thought about having it chambered with a 0.337 tight neck and a 1.5 degree leade like joelkdouglas just in case that 0.003 and 1.5 degree less slope might really matter some day. But decided the 0.5" slower twist should make up the difference.

shootem, here's a link to a post on another forum from Bryan Litz, last I knew to be the head ballistician at Berger. It will give you more to think about re:twist.

http://www.longrangehunting.com/forums/f19/nosler-lr-accubonds-bc-testing-results-137554/

I don't know that this post infers that a faster twist rate will increase the BC of a bullet, but I interpret it does say a slower (insufficient) twist rate might decrease the BC of a bullet. That reduction would not have an appreciable impact for me, but for long range shooters it very well might.

My friend, the late Don Miller, developed the twist formula used by JBM and included in the ballistic program Liz includes when you buy his book, APPLIED BALLISTICS FOR LONG-RANGE SHOOTING. But even Don (and Bryan) admit some aspects of twist just can't be accounted for in formulas, due to slight differences in bullet shape and balance, and probably rifling and crown as well.

But the Miller formula beats the hell out of the Greenhill formula, or any other simpler formula.

Thanks for the link joel. Some good stuff in that thread. Wish he had been able to test the 190 & 210 .308 .

So...should a person toss out the length of the plastic tip...its actually a little substantial in some bullets....but sure wouldn't seem to weigh enough to affect anything?

Do note the page mentions the equation used has been shown by Miller to be inaccurate. I have a copy of Miller's equations somewhere for use someday on the update to that page. For a rifle, Greenhill's equation is well out of it's sweet spot, namely howitzer shells of rather poor aerodynamic form at modest speeds.

Well, mine and most BR shooters use 17-19 twist barrels on their 30BR barrels shooting 115-125 grain bullets. My Grandson's 30BR hunting rifle has a 15 twist and he hunts with 125 grain bullets. I have a 11.25 twist Obermeyer barrel to shoot 200 grain bullets out of a 30 cal. I haven't checked the bullet recommendations for these twist. O/A bullet length and o'give figures into this. VLD bullets of the same weight of say a flat base bullet will need additional twist rate.