Each of {HEAD ~ said walls} defining {TAIL ~ a secondary receiver chamber} sized to receive a magazine cartridge of rounds a shorter length than otherwise provided for in a rifle 
defining
Each of { HEAD ~ said walls } defining { TAIL ~ a secondary receiver chamber } sized to receive a magazine cartridge of rounds a shorter length than otherwise provided for in a rifle
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH