Gunsmithing My new build! 30-338 LM or maybe Improved?? Help!

[PGWTW338]

Like the title says need suggestions! I will be building it myself with supervision from my friend who is a gunsmith

Using his shop as well!
Very generous of him I have always wanted to do this! Of course I do have a machining and mechanical background but always like to learn new things.

My first question is what would be the minimum length of barrel to get in and around the 3300-3400 FPS with 208 AMAX will this be possible? We will be probably using Broughton. As far as twist rate is 1-10 a good start or should we go faster I would like to try some 240 SMK? Any tips on Reamer dimensions? I will be talking with Dave from PTG soon. We do plan on gaining extra case capacity by using a uni-throater tool and hanging the 208's out further. I also do not want to neck turn so want to keep neck clearance at .004"+ and are still not sure if we should go the improved route.

I would really appreciate some of your input I know there is a wealth of knowledge here that could definitely help with this build. The build will be using the .338 Stiller action McMillan A-5 LA stock.

 

[Idaho CTD]

Re: My new build! 30-338 LM or maybe Improved?? Help!

The IMP. version will have less case stretch and more capacity. If 208 Amax's are the lightest bullet you want to shoot you can have it throated for that particular bullet.

 

[LRI]

Re: My new build! 30-338 LM or maybe Improved?? Help!

I have built/owned a 300/338 La poo poo.

I set mine up for 125 grain Ballistic tips. (dog gun)

4375fps was the peak velocity according to Cor Bon's chronograph/tunnel.

I had a 1:12 barrel.

I have the reamer but I don't rent/lend tools. If you get stuck, we'd be happy to fit it up for you.

C.

 

[Goin'Hot]

Re: My new build! 30-338 LM or maybe Improved?? Help!

If you're dead set on running 240's, you'll need to stick with the 10 twist. If you just want to zing the 208's, an 11 twist would be better. Go with a 32" barrel to gain some added velocity. With a 32" 11 twist barrel, you'll have plenty of boiler room to get the 208's past 3300. I don't know if you'll get them up to 3400 though.

I'd recommend calling Hornady to find out what kind of rotational torque the 208's will take. Spin them too fast and they'll blow themselves up when they exit the barrel...

 

[DAVETOOLEY]

Re: My new build! 30-338 LM or maybe Improved?? Help!

208's will work in a 1-12 but with all that capacity you'll have go with heavier bullets. I've been building an Imp version for years, good round for heavy bullets. Too much capacity for pure accuracy work. The lazy way out is the 300 Norma. No fire forming or sizing down. 208's @ about 3150-3200 FPS w/ 27" barrel. Go to 30" and you could pick up another 50-75 FPS.
The further you get past 3000 FPS the more accuracy suffers with these large calibers.