So I have bought a CM16 with two "P mags", whatever they are. I have no idea what makes these different from normal mags other than the raised bits. I also have no idea what capacity these are or who makes them. They have the Magpul logo, but I suppose could just be licensed as Magpul do make RS weapon parts. I can't see any hatch to pour in BB's, and also have no idea what the little button on the bottom does, as the bottom doesn't seem to move at all when it's pressed in. Any help at all would be great here as I don't know WHAT I have.