Optimum Barrel Length for 338 Lapua Mag

[jburnette]

I'm designing a 338 Lapua Mag bulpup (clean sheet of Paper)and want to get 3000 fps from a 300 grain Scennar bullet. Anybody got any practical experence with this topic? I have the barrel set at 30" now plus a muzzel brake. Also is there a rule of thumb ratio for the velocity gain the brake adds? I realize there are a bunch of brake designs out there and the vented area is key but all I need is rule of thumb for now.

Thanks,
James
burnettearms.com

 

[TimResin]

Re: Optimum Barrel Length for 338 Lapua Mag

Your probalby going to have to go with a Ackley Improved .338 Lapua with that kind of speed.

 

[snipedogg]

Re: Optimum Barrel Length for 338 Lapua Mag

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TimResin</div><div class="ubbcode-body">Your probalby going to have to go with a Ackley Improved .338 Lapua with that kind of speed. </div></div>

Agreed.

The average 338 Lapua with the 300grainers will net you around 2700-2750. With a 30" barrel you could push around 2850 from what I've seen and that's pushing it. The AI is your best bet to push them that fast. Which leads me to my next question: why are you set at pushing them that fast?

 

[Goin'Hot]

Re: Optimum Barrel Length for 338 Lapua Mag

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jburnette</div><div class="ubbcode-body">Also is there a rule of thumb ratio for the velocity gain the brake adds? I realize there are a bunch of brake designs out there and the vented area is key but all I need is rule of thumb for now.</div></div>

I'm not aware of the brake adding velocity. I agree with the above posters. If you're looking for 3k out of the 300's you'll need to go with an improved case. I have a buddy with a 338 rogue (37° shoulder) and he's getting the stock paint finished up. When it's back together, we'll post some velocity results.

I ran some data through quickload and found 1" OF BARREL results in about a 20 fps gain in velocity. I was using Retumbo for my powder and the Scenar for the bullet.

 

[jburnette]

Re: Optimum Barrel Length for 338 Lapua Mag

Thanks guys,
I thought that 3k would be acheavable just by adding more powder, slighty longe barrel and using a super stronge action. I guess it's like trying to get 3K out of my 29" barreled 308 with a 155 palma bullet. 2900 is no problem but that takes a full case to the top of varget and the primer is starting to show signs of excess pressure at that point (great groups though). I googled the 338 rouge and the version I found was a 378 weatherby necked down to 338 without the weird radii on the shoulder. The guy said it was capable of 3k but the Berger 300's he was shooting were coming apart at that velocity so he had settled for 2800 for now. He said berger had a gen 2 300 that will fix the problem. I want to stick with the 338 lapua for now that way I will be able to benchmark it against rifles without any cartridge variables to argue about. I will probably cut the barrel back to 28" if it doesn't mess up the rifles center of gravity to bad. It will be easier to get a barrel blank also.

Thanks,
James
burnettearms.com

 

[snipedogg]

Re: Optimum Barrel Length for 338 Lapua Mag

I'm still curious why you want to push them so fast. What do you need to do with 3000 fps that you can't do with them going 2750?

 

[PowerstrokeOBX]

Re: Optimum Barrel Length for 338 Lapua Mag

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jburnette</div><div class="ubbcode-body">Thanks guys,
I thought that 3k would be acheavable just by adding more powder, slighty longe barrel and using a super stronge action. I guess it's like trying to get 3K out of my 29" barreled 308 with a 155 palma bullet. 2900 is no problem but that takes a full case to the top of varget and the primer is starting to show signs of excess pressure at that point (great groups though). I googled the 338 rouge and the version I found was a 378 weatherby necked down to 338 without the weird radii on the shoulder. The guy said it was capable of 3k but the Berger 300's he was shooting were coming apart at that velocity so he had settled for 2800 for now. He said berger had a gen 2 300 that will fix the problem. I want to stick with the 338 lapua for now that way I will be able to benchmark it against rifles without any cartridge variables to argue about. I will probably cut the barrel back to 28" if it doesn't mess up the rifles center of gravity to bad. It will be easier to get a barrel blank also.

Thanks,
James
burnettearms.com </div></div>

That sounds like the Kahn.

338 Kahn
338 excaliber
338 yellow bastard (uses a .50 bmg case)

Doesn't the 378 have that funky rounded case?

 

[jburnette]

Re: Optimum Barrel Length for 338 Lapua Mag

3000 is 9% faster I don't have a ballistics program handy anymore but from what I remember that's the difference from a hit or miss at 1000 yards. I probably will experiment later on with an Ackely version. The Lapua case has quite a bit of body taper and small shoulder angle and strong web perfect for improving. Seems like the 40 cals have the best balistics but I can't imagine how expensive the components are.

 

[Goin'Hot]

Re: Optimum Barrel Length for 338 Lapua Mag

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jburnette</div><div class="ubbcode-body">I googled the 338 rouge and the version I found was a 378 weatherby necked down to 338 without the weird radii on the shoulder. </div></div>

Call PTG and see if they will email you a print of their 338 Lapua Rogue reamer. It's a 338 Lapua with the body taper removed and the shoulder blown out to 37 degrees. I'll try and get a water capacity of the case for you over the next couple days.

 

[SVG308]

Re: Optimum Barrel Length for 338 Lapua Mag

The 338 Lapua Improved will get you to 3,000fps w/ a 300g Berger. Go with a 30 or 32" barrel and you'll be there.

 

[71firebird400]

Re: Optimum Barrel Length for 338 Lapua Mag

You thought 3000FPS was realistic with a 300gr 338LM, and that muzzle brakes increased velocity?

And you're "designing" a rifle?


Riiiiiightttt

 

[jburnette]

Re: Optimum Barrel Length for 338 Lapua Mag

Thanks for the helpful input guys. If anyone would like to look at the design so far go to burnettearms.com. You will find some images of the bullpup along with a couple of target rifles I designed and machined. Also take a look at the barrett 98b 338LM. I designed about 80% of it in the summer of 2006.

James

 

[snipedogg]

Re: Optimum Barrel Length for 338 Lapua Mag

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jburnette</div><div class="ubbcode-body">Thanks for the helpful input guys. If anyone would like to look at the design so far go to burnettearms.com. You will find some images of the bullpup along with a couple of target rifles I designed and machined. Also take a look at the barrett 98b 338LM. I designed about 80% of it in the summer of 2006.

James </div></div>

So you designed a bunch of rifles (including a Barrett) and thought a muzzle break increased velocity?? Your site is a bunch of animated designs, nothing real, which is what your making it out to be.

I'd recommend staying far away from a lathe and let a good smith do the build and recommend a cartridge for you.

 

[Dark Horse]

Re: Optimum Barrel Length for 338 Lapua Mag

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jburnette</div><div class="ubbcode-body">3000 is 9% faster I don't have a ballistics program handy anymore but from what I remember that's the difference from a hit or miss at 1000 yards. I probably will experiment later on with an Ackely version. The Lapua case has quite a bit of body taper and small shoulder angle and strong web perfect for improving. Seems like the 40 cals have the best balistics but I can't imagine how expensive the components are. </div></div>

Why don't you try loading the Lapua to it's intended velocity and just adjust your elevation 9% higher?

You seem to focused on building a rifle around the factor that matters least when it comes to making hits.

 

[71firebird400]

Re: Optimum Barrel Length for 338 Lapua Mag

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dark Horse</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jburnette</div><div class="ubbcode-body">3000 is 9% faster I don't have a ballistics program handy anymore but from what I remember that's the difference from a hit or miss at 1000 yards. I probably will experiment later on with an Ackely version. The Lapua case has quite a bit of body taper and small shoulder angle and strong web perfect for improving. Seems like the 40 cals have the best balistics but I can't imagine how expensive the components are. </div></div>

Why don't you try loading the Lapua to it's intended velocity and just adjust your elevation 9% higher?

You seem to focused on building a rifle around the factor that matters least when it comes to making hits. </div></div>

Don't even both trying....this self proclaimed gun designer thinks that you can push a cartridge beyond it's limitations by "using a super stronge action". Have fun hammering the cases out of that "stronge" action.

Maybe you should go work on that velocity increasing muzzle brake a little more; perhaps that'll push you to 3000FPS?

 

[bench98]

Re: Optimum Barrel Length for 338 Lapua Mag

If I read your post right you designed the Barrett 98 and don't know about muzzle brakes....Who are you trying to kid? Chris Barrett is the man.