6mmAR?

It's no secret here, I'm a big fan of the 6mm bore in many variations. The 6x45/6mm-223 Rem is a nice option for heavier slugs with good velocity. 80gr feeding from the mag, can't be too bad methinks! A wildcat based on a necked 6.8 to make it 6mm SPC, for all intents and purposes, would gain the short barrel benefits of the 6.8 but benefit in itself with lighter slugs (80-90gr nominal weight), more velocity and increased effective range over its parent 6.8 case.

I read up on the 6mm AR awhile back, even talked to its inventor on the phone about it and mentioned the XCR. To really take advantage of what the cartridge offers you'd have to use long ogive bullets and for 6mm that means 107gr typically. The lighter round would gain a touch more case capacity over the 120+gr 6.5 tips. You could probably use some lighter slugs (87-90gr) with more standard ogives and get impressive velocities but the shortened OAL would worry me in terms of reliable feeding and chambering as the rounds would have more room to get jostled around in the mag.

In the end however, I fully realize these rounds are for more limited and specific uses and that's about as far as they'd ever go. As long as 5.56 is the pill of choice (with the prices to match) it'll just be simple economics that it'll remain king for some years to come, even if a new military cartridge is announced tomorrow, it'd take a long time for surplused cases to make it into the commercial realm for the reloaders and for the market to want the next best thing to have any impact on pricing. Even the "SHTF" crowd that worries about such things realizes that they may be better rounds but I guarantee that if it came to that 223 would be easier to scrounge than 6.5G, 6.8 SPC or any of that other stuff.