I am intrigued by the SIG 556 R in 7.62x39. I like the round better than 5.56 and I like the "look and feel" of the Sig 556. How do they function? How do they hold up? I am not looking for an AR-15 or another AK. I was wondering if anyone who has one of these, or has fired one (or even the 5.56 version) could provide me with information I can't get from the manufacturer.