The MK3A1 is pretty fun. With extended mags it can hold 14 bullets ( that's with one loaded already ) two more than the USAS if I'm remembering correctly. It can also equip a suppressor, but it doesn't physically show up and it sure doesn't sound silenced. I'm not to sure if it actually gets the benefits of equipping a suppressor. It also fires a little slower than the USAS and has a bit more recoil.