Just stay away from their .458 socoms. They're cheap and tempting, but ~8 people bought uppers in a group I'm in, and 0 ran out of the box. The one that was finally tweaked to running right was sent to Tromix to go over. I was surprised Tony took it to massage. Very glad I went with tromix for mine, it's been flawless and lays the smack down on deer and hogs out to ~150.
Definitely didn't know they came out with long action ARs, interesting. I'll keep my eye on the guinea pigs, I'd love a 300wm AR for no real practical reason!