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Other Calibers in LR-308 pattern rifles


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Here's a little something that's been on my mind lately. I'll probably never put the idea to actual use, but an interesting thought experiment if nothing else.

We've seen all kinds of stuff in the AR-15, and even invented some rounds for the gun like .50 Beowulf, 6.8 SPC etc. and that's in addition to all the other stuff that'll fit it with just a barrel change and a few minor adjustments.

So my thought is, why not do it for the LR-308? I know there are a few already out there such as .243 Magnum and all, but I'm wondering, where could we actually take it? Also, I'm wondering if we can't bottleneck something very big like a .50BMG or .460 Weatherby down to a .338 to get the ballistics of a .338 Lapua out of the gun.

  Anyway, I'd like to hear your thoughts on this.

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Well, it would have to be a cartridge that is considered a "short-action" round for bolt-action rifles, e.g., .243 Win, .308 Win, etc.

Maybe .338 WSM?  Open that up to a .375, .400, .450, .475, and/or .500.

Just on a .308 case, how far have they opened that up?  The biggest I'm aware of is the .358 Win, though the .338 Federal is supposed to develop quite a bit more muzzle energy.

I'd like to see something along the same lines as the .300 Whisper based upon the .308 case (the .338 WSM could probably make something REALLY effective!), wherein the case is opened up to basically the width of the body and pushing a bullet of that diameter.  In the case of a .308 case, pushing a .454/8 diameter slug of 450 grains at just under the speed of sound...we could get cute and call it a Whisper, but the .450 THUMP sounds better.

By law we would be regulated to a .500 diameter bullet in a WSM based case...so a limitation of what...600 grains?  It would probably be worth paying a licensing fee to call it something like the ".500 Sante Fe Locomotive". 

Sorry Senor Terrorist...your Russian issue bullet proof vest doesn't count anymore.


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I think I already posted something like this before - a list of short action rounds that have been applied to semi-auto rifles.  It's somewhere here...  <dontknow>

Found it...

Here's a list of what you'll be able to shoot through the big-bore AR.  This may or may not be all-inclusive - I have no idea how many new calibers, and wildcats, come out everyday...

.243 Win

.260 Rem


.270 WSM








.300 Savage

.300 Remington Short Magnum

.338 Federal

.358 Win

.450 Marlin

.470 Rhino

.500 Phantom

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I've been told that the .338 Ruger compact magnum (.338 RCM) is ballistically superior to the .338 Federal, and will also chamber in the large platform AR. Anyone know anything about this cartridge?

I've only read the articles.  Ruger puts this round in their Compact Magnum M77 rifle.  The case is based on a shortened .375 Ruger Magnum.  You would probably be able to keep a fairly high magazine capacity too.


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I've been told that the .338 Ruger compact magnum (.338 RCM) is ballistically superior to the .338 Federal, and will also chamber in the large platform AR. Anyone know anything about this cartridge?

The benefit of the 338 Fed over the RCM is the casing. The 338 Fed uses the same bcg and mags as the 308. All that req'd to convert is a new barrel, or have a gunsmith bore out and rechamber your existing barrel for about $150.

The RCM would need a new bolt, possibly a different buffer system, barrel, and customized magazines.

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Do you know what the parent case is for the .338 RCM? I certainly can appreciate the commonality of components as the 300BLK has with .223, but I'm wondering if there's enough ballistic superiority over the .338 federal to recommend it. I'm trying to come up with something to get me interested in a new large platform AR build, and I'm thinking that a different caliber (if I can find the right one) might do it. The two logical directions seem to be, either go for a max range cal like .260 or 6.5 BR or go for the most powerful long range cal I can come up with, which right now seems to be one of the .338 short action cartridges.

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