An assembly for rapid loading and feeding of paintballs in a paintball marker comprises a receiver mountable on the marker, having an opening to receive and secure a magazine carrying paintballs, and a gate opening mechanism to open the magazine, releasing the paintballs. An ejection mechanism to clear a magazine from the opening may also be provided. The magazine comprises a resiliently biased gate mechanism to protect the paintballs until the magazine is inserted into the receiver. The magazine may be opened to refill it with paintballs, and may be disassembled for cleaning or maintenance.