303 British Chamber Diagram

[Bruce_in_Oz]

CNC turned solid bronze with several grooves to accommodate the metal displaced by the lands? Look, Ma; NO LEAD!!

Good point about the Cordite as well. It burns fairly quickly compared to modern ideas about "ideal" burn rates.

However, given that the U.S. and Canada made vast quantities of "Mk7" ball ammo, in BOTH world wars, What were they using to fill all those millions of rounds?

Some Canadian production used Cordite propellant and Mercuric primers, but to the best of my knowledge ALL U.S. production was fuelled by granulated, double-based Nitro-Cellulose propellants and ignited by lead-based Boxer primers.

And then there is the substantial output of .303 Ball and Tracer from the FN plant, especially post WW2. I suspect that they would have put some effort into matching "standard" Mk7 ballistics at least for the ball ammo, especially as much of this production was shipped in cases and packets labelled, "Pour BREN".