Optmum twist??

[clickbangreload]

Don't laugh, but I am building a mild bolt action hunting gun based on the 7.62x39 case and a .308 bore barrel. I'll be using Lapua brass and 125 grain .308 bullets. The velocity will be typically 2400 FPS.

After reading all the info on the 30BR on this site, I thought it best to seek advice on the twist
rate for the barrel. How can I determine an optimum twist rate? What would be the slowest twist
that will stabilize a 125 grain .308 bullet at 2400 FPS??

Thanks for the help.
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[MQ1]

I will not laugh...sounds like an interesting project.

Go here to plunk your data into a Greenhill formula based chart:

http://www.montanabulletworks.com/page11.html

I would consider going with a .300 Savage...an old round, but stupid accurate...If this is a hunting rifle I'd go with a minimum of an 11 or 12 Twist...you may want to bag an Elk someday....

MQ1

 

[clickbangreload]

Well, this gun is for a very limited use - no big game. I will check out the twist calculator. I was hoping
for some practical advice, maybe from a 30 BR shooter. Thanks for your input.

 

[MQ1]

What kind of game are you hunting?

MQ1

 

[jonbearman]

I built a savage 7.62x39 gun with a mcgowen 1 in10 twist barrel. The only thing I did wrong was having the .310 bore which uses the odd bullets. However with sierra 125 pro hunters it is a hammer.

 

[Dusty Stevens]

14 or 15tw will work well with 125. We use 17-18 for 112-118 but that is for custom bullets. You'll need to compare the lengths of the bullet you'll be using to a custom bullet to get a gauge on twist rates

 

[mac86951]

I will not laugh...sounds like an interesting project.

Go here to plunk your data into a Greenhill formula based chart:

http://www.montanabulletworks.com/page11.html

I would consider going with a .300 Savage...an old round, but stupid accurate...If this is a hunting rifle I'd go with a minimum of an 11 or 12 Twist...you may want to bag an Elk someday....

MQ1

+1 to 11 or 12 twist, which should work well if you want to use cast bullets in mild loads too.

-Mac

 

[Swampbuck]

I would go a 12 twist or 11.25. That will do 125-175 grain bullets. Why limit yourself.

 

[clickbangreload]

Thanks to everyone for your replies. As for the intended game, it is sage rats, jack rabbits, badgers, blacktailed deer, and coyotes at short range. I'll use both cast and jacketed. I already have a Ruger M77 in 7.62x39 and a CZ-527 in 7.62x39. Neither rifle has a .308 barrel. I just wanted to have a better selection of bullets than what is currently available in .311. I was toying with a 30 BR, but I already have thousands of rounds of brass with a thousand Lapua cases on the way. I also have a lifetime supply of W680 powder as well as a lot 1680 and 335.

Again, thanks for the input.

 

[Tim Singleton]

You may have a reamer in 7.62x39.
If not I would go with a 30 major with a 17 twist

Search 30 major on here

 

[jonbearman]

Swamp buck where did you get loads for the 175 grain bullets?

 

[Swampbuck]

My 1-12 twist rifles do fine with federal 175 SMK or duplicate hand loads. But that is maxing out the 12 twist. 11.25 might be a little safer as some 1-12 barrels may not like above 168 grain SMK.

 

[butchlambert]

Billy Stevens chambered a 30BR for my Grandson many years ago. He shoots 125 BT through it. It is a 15 twist and is incredibly accurate. Josh has had a huge amount of 1 shot kills to 300yds. Only 2 shot kill was a coyote. Josh shot it and he hit the ground. We walked up to it and Josh poked him with the barrel and the coyote jumped up. One more shot and he was down for the count.