When {HEAD ~ the breech block} is in the locked position, the locking element is supported by the control member and engages {TAIL ~ the stationary locking surface} 
When { HEAD ~ the breech block } is in the locked position , the locking element is supported by the control member and engages { TAIL ~ the stationary locking surface }
OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL