God bless 'em for thinking outside the box and all ... but lets be honest we smack the cat with a rolled up newspaper for thinking outside the box.
Honestly, I've shot a couple AR pistols and I never found the recoil of the 5.56mm to be so bad that I couldn't just jam the end of the buffer tube into my shoulder and be just fine (especially if the have one of those foam socks on them).
