The 556R will not shoot Wolf ammo nor will it accept a steel mag without doing obvious damage to the weapon over a short period. I did read the one review from Warrior Talk that stated it would shoot anything in terms of ammo, but I have read many noting failures. Plus, Sig says they will void your warranty to shoot steel casing.
That's the "gen one" rifles. The new ones have a steel insert to protect the receiver from wear by the magazines. And SIG says you can shoot any 7.62x39 in the new one.
I know, if you do a google search you find lots of critical reviews and lots of problems. But look at dates. I don't actually own one so I'm just telling you what I've observed online. The newer ones are worth owning. I would take one anytime. Maybe I'll get the chance someday if the chaos ever goes away!