When {HEAD ~ the breech block} is in {TAIL ~ the release position}, the locking element is released by the control member which moves in the breech block parallel to the breech block 
is in
When { HEAD ~ the breech block } is in { TAIL ~ the release position } , the locking element is released by the control member which moves in the breech block parallel to the breech block
OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL 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 OTH OTH OTH