It's a "Krinkov" replica, otherwise known as an AKS-74U, chambered in 5.45x39mm. That thing on the front is a flash hider. It's very loud. It's a very short barrel, obviously, but that's what the "U" is supposed to be -- for folks who need a rifle but work in a vehicle (like a tank), or a paratrooper.

Probably not useful for hunting anything but fun nevertheless, and surplus Russian ammo is so much cheaper than Nitro loads!