I know there really is enough rounds for the AR platform that it will give you a headache just from trying to keep up. Now there is yet another round in R&D out there. Although the .375 Reaper is still in its infancy, there are various AR forums that are calling it the next .300BLK round and a contender to the .458 SOCOM. While I am not sure I agree with that, ballistics have always been fascinating to me, and building rounds is how we innovate and down the road save lives with better rounds for the police and military.
The case for the .375 Reaper is made from .308 brass that is cut down in length and then necked down to accept a .375 bullet. The round will also fit standard AR15 magazines, but your 30rd magazine becomes a 15rd magazine with the .375 Reaper. All that the end user would need to replace would be the bolt and barrel to be able to accept the new round. So just like being able to switch from 5.56 NATO to .300BLK just by changing the upper, this round would offer the same modular ability to the end user.
Because the round is still in the R&D phase, there are no official ballistics yet (that I was able to find) but I can imagine that the round, much like the .300BLK will be a big, slower moving round that will hit very hard and be dedicated to CQB shooting and inside of 300m. Reading through comments that W3 Precision has made, it looks like it will probably end up being a 200gr Spitzer bullet with a MV around 2300-2400fps, but of course that is (as always) subject to change.
Using the Applied Ballistics online calulator, I was able to build a mock round with a 200gr Spitzer bullet to show some of the possible ballistics. Here are the ballistics based on some rough numbers. The round begins to drop off at 300yds with a 22in drop, but at 400yds you end up with a bullet drop of 4 feet. Inside of 100yds the energy is right up there with a .308WIN and well over that of the .300BLK 220gr bullet (498ft-lbs). We will have to wait for official ballistics to come out, but early number look promising.
I will admit, my first reaction is that this is yet another round for the AR platform, but one that could be one to watch. The numbers are definitely interesting, and lend credence to the round being viable for various uses. Many are watching the round as a contender against the .458 SOCOM, the .375 Reaper being a cheaper alternative using more readily available brass instead of proprietary brass. If you are interested in keeping an eye on the progress, Whiskey 3 Precision Systems is posting updates on their Facebook page http://www.facebook.com/W3PrecisionSystems and has some other links listed to follow the progress.