It looks like the hottest new thing these days is the new cartridge .300 AAC Blackout. It's designed to offer hard-hitting performance out of a short barrel at relatively close (300 yards or less) ranges, but what makes it different from big-bore cartridges like the .50 Beowulf is its reasonable pricing, and the fact that it can fire from an almost unmodified AR-15--all it requires is a barrel change, because 5.56mm bolts, magazines, and other components will safely perform with .300 AAC Blackout.

Apart from that, when suppressed, its subsonic rounds are both very quiet and quite powerful.

I've been following this thread on THR and to be honest, I am somewhat impressed in the idea of such a round. Sure, it'll never be as popular as .223, but I think there's certainly a niche for it. Some people have used it for hunting with good results, and why not? Most shots fired in hunting scenarios are fired at targets within a hundred or two hundred meters of the hunter, well within .300 AAC BLK's niche. Apart from that, I feel certain that when people really start to play with reloading for it, we'll get better and better rounds for less and less $$$.

Here's the round's official propaganda site: http://300aacblackout.com/

Have a gander and post here about your thoughts with respect to the .300 AAC Blackout round.