So, ID'ing the gun had me stumped for a bit - I recognized that huge trigger guard from somewhere, but I couldn't for the love of me tell where. Then, it dawned on me: It's an "R9-Arms" submachine gun! It doesn't really have an actual name, and I don't know how you'd tag it, but I'm going to go with r9_arms_(gun).
Just wanted to note this because it's a pretty interesting gun. Cheers.