It comprises {HEAD ~ a receiver assembly} 22, having an upper chamber 24 for receiving {TAIL ~ a bolt assembly} 26 
It comprises { HEAD ~ a receiver assembly } 22 , having an upper chamber 24 for receiving { TAIL ~ a bolt assembly } 26
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH