This is an interesting Air rifle made by a company called RAP4 "Real Action Paintball", This RAP5 started out life as a .43 caliber paintball gun but mine was converted (using the factory conversion kit) to fire 4.5mm steel BB's. I ordered mine already converted this way. The RAP5 is an MP5 replica and shoots in both semi and full auto modes complete with ejecting plastic BB casings.