The L4 guns in service that had already had a previous life as Mk2 or 3 Brens suffered from worn out breech block stops in a big way. In order that the breech block never touched the face of the barrel we were permitted to stone/grind the upper front face of the breech blocks in order to remain clear of the barrel face BUT stop on the breech block stops. That's the reason why you might see this effect on used breech blocks and wonder why. There was a minimum depth of cartridge seating permitted but it was quite generous.
This was also allowed for on the .303" Brens too BUT (and am going from memory now.....) because there were a top overhanging feed horns on the .;303" Bren breech blocks, this was only done on a specially set-up horizontal grinder.
I think that at the end of their lives, worn-out breech block stops were the biggest killers of Brens and L4's especially if they had been using live service guns in training instead of using the already worn out L54 and L55 drill purpose guns. You could tell them until they were blue in the face but...............
Interesting thread!
