The locking mechanism has {HEAD ~ a breech block} which is locked with {TAIL ~ the stock} and which can be released by a spring biased control member 
is locked with
The locking mechanism has { HEAD ~ a breech block } which is locked with { TAIL ~ the stock } and which can be released by a spring biased control member
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH