375/308

[Lone spur]

I should start by saying I am very new to wildcatting but just as interested in learning. That being said, is a 375/308 possible? Has it been done? (If it is possible, I have to imagine it's been done.)
The reason I ask is that I was discussing possibilities with a friend and he thought I would have a good 300/221-like potential in an AR-10 based system.

[Blackhawk44]

I am reasonably sure that it has been done before (though not likely on an AR chassis), your problem will be bullet performance on target since most bullets for the .375 bore are designed to perform at a velocity higher than you will be able to attain in the .308 case.  If performance closer to that of a solid bullet will suit you then have at it.

[Catfish]

It is about the max. that makes sence. I have the 06 case, which is the same as the 308 but just longer, necked out to .411. To do that you must make it very near a straight walled case and then you only have .009 shoulder to head space on and the shoulders bump back far to easily.

[mcwoodduck]

Looking in the Cartridges of the World there is a 375 Whelen and an Ackley Improved version as well.  So my guess is that the answer is that it can be done with a 308 case.  My only concern is that it may not be possible with the AR 10 platform.  The larger bullets may exceed your mag over all length.  Or you will have to go with very light bullets.  If your looking for 235 or smaller bullets.  I think you may be better off with either 338 or 358 and making an Ackley Improved version.  Also smaller bullets than 270 are designed for the 375 Win or 38-55 and may have a big flat front that may be difficult to feed in an auto with an almost strait wall.
Sounds great as a thumper bear, moose, pig or camp cannon bolt gun.
You may have a better time with the 300WSM or 30/338 Ruger case ( not sure if this case is too large for the bolt of the AR 10) and necking it up giving you a larger shoulder for the flat nose light 375 bullets  They have put the 300WSM in the AR 10 platform and with a simple barrel change you could have both.

[Blackhawk44]

For an AR thumper, why not go right to the top?  Get an upper for .458 SOCOM.  Offers a much wider selection of bullets built for various velocities.  Well beyond the .450 Bushmaster or .50 Beowolf.  Even with a 235gr bullet in your .375/08, I doubt that velocity would beat 2300fps, so you would'nt be giving up that much range to the SOCOM.  Just something else to think about.   

[Reed1911]

I cannot see why not to do it. I have a .375SM that has much less capacity and dows very well with 200g Sierra's and 220g Hornady's as well as some custom bullets from Hawk and lead bullets. Really the 225g SSP from Hornady would be excellent from an AR platform launched at +/- 2000FPS it would be a hit! The 250-300 range may require seating deep, or you could cut the chamber to house a slightly pushed back shoulder for fit, but once you get to that weight I think you'd end up with bullets too tough for expansion at the velocities you'll be running. 2000-2100 should be about right from the .308 case with the 200-225 weight.

[Lone spur]

For an AR thumper, why not go right to the top?  Get an upper for .458 SOCOM.

Actually, I got the 458 SOCOM upper for my Rock River back in January. It's been my favorite rifle since the first pull of the trigger. I have set up as a bear/boar gun with a 1-3X Weaver for getting on target quickly. The idea of the 375/308 was simply the result of mental calisthenics between a friend and I. Thanks to everyone for they're input.
By the way, Mr. Reed makes some mighty fine ammunition for the 458.