you should absolutly get one, now on terms of size brand and model, im not evensure, but to put it in you should be able to just push the forward release like the real m4 and then pop uot the back pin, then with alittle forcethe upper and lower reciever should open like a hinge, the hinge part being the front pin, at this time you should be ale to see the barrel, tell me if you have any problems with that.