The breech block has {HEAD ~ at least one bore} which receives {TAIL ~ a locking element} supported for radial movement in the bore 
receives
The breech block has { HEAD ~ at least one bore } which receives { TAIL ~ a locking element } supported for radial movement in the bore
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH