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