Hey guys check this site out!
http://www.realguns.com/calc/riflingtwist

Just found it during my nightly surf of the www.

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Why not just put a piece of tape on a cleaning rod and when it flags up (takes a full turn) you have the answer, regardless of load or whatever, or am I missing something?

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Ray Atkinson

ray@atkinsonhunting.com
atkinsonhunting.com

This calcalator tells me to use a twist rate of 21.3 : 1 in my 308 Winchester with (.800) 110gr. sierra HP. The same would go for my 30-378 Wtby. Is this realistic?

Andrew V. McGee

I use a twist calculator like this a lot. The twist required by the short 110 gr Sierra is correct. The value of the calculator lies in finding the right bullet length for the twist you have. Measure the twist of your rifle, then fiddle with the bullet length on the calculator till you get a rate of twist that is one inch slower than what you have. (If your rifle measures one in twelve, use a bullet that requires one in thirteen). That is generally the best bullet for hunting. A longer bullet that gives exactly the right rate of twist is best for very long shots.

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Gerard Schultz
GS Custom Bullets

Gerard,
So within certain limits of velocity and bullet length, the formula generated twist rate is O.K., for barrel selection purposes, or as a guide to matching the barrel you have to the proper length of the bullet.

It does show that the minimum twist rate required does get faster as velocity decreases and bullet length increases.

Does the overall length of the bullet require any sort of correction factor or "form factor" depending on whether it is a sleek and pointy boat tail versus a blunt and flat based one?

For example, would the same twist rate apply to bullets of the same weight in the FN and HV GSC bullets, or should one go with the faster twist required by the longer HV, and be happy with the greater penetration this might give at close range with the stubbier FN? I think I have answered my own question. Sounds like a plan.

BTW, I sent you an email about my 475 caliber 500 grain HV and FN bullets not having arrived here yet. Did you get it?

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Rifles And Bullets r us: RAB

I am trying to find a a mathematical equation that will tell me if a 1 in 12 twist is better in the 338-06 than the .338 bore standard 1 in 10 IF all you are going to shoot is the 200 & 210 gr. bullets. I'm Trying to keep the horse in front of the cart here & not spend the $$$ on a barrel that is not going to give me the performance i'm looking for. With the standard 1 in 10 twist for 338 caliber the heaver bullets always perform better than the lighter bullets. I have built several 338-06's with the standard 1 in 10 twist barrels. They all performed best with the heavier pills. I'm betting a 1 in 12 will do the trick.

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Ron,
You have answered your own question indeed. Your e-mail came in on Friday, I think, but we spent a couple of days away from work. If you do not have them yet, the black hole has them and I will ship more on Wednesday. We were out of 470 500 gr HVs and are running them on night shift this evening.

Bear Claw,
The 338 Lapua magnum is designed to a one in twelve twist and originally as a sniper caliber. One must consider that a 338-06 is not intended for sniper use and rather for closer shooting. A one in ten will allow you to shoot the full range of available 338 bullets with good results and better penetration than a one in twelve. One in twelve will allow a bullet of the correct length to nose over correctly at extreme ranges for better accuracy. With a one in ten twist, the combination of bullet length, speed required for a reasonable trajectory and lowest wind drift, available case capacity and so on, makes for lesser extreme range performance. Extreme range performance from a one in ten will require a jacketed lead bullet of close to 300 grains and a monometal bullet of about 250 grains. You would need a BIG case to make such heavy bullets go fast enough to get the distance. My choice for a 338-06 would be one in ten. In SA we have a caliber called 338 Sabi (ballistic twin to a 338-06) and it is very effective on large animals with a 180 grain monometal bullet. Penetration is way beyond what is expected and exceeds that of jacketed 250 grain bullets. It is a shining example of overtwist at work.

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Gerard Schultz
GS Custom Bullets

Thanks to all for the responses. This is an interesting subject to say the least.

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