When {HEAD ~ the breech block} is in {TAIL ~ the locked position}, a clearance is provided between the locking surface and the locking element on the side facing away from the barrel 
is in
When { HEAD ~ the breech block } is in { TAIL ~ the locked position } , a clearance is provided between the locking surface and the locking element on the side facing away from the barrel
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