I use to have a B.S.A. in .310 Cadet and marked "Q" for Queensland.

I used .318" diameter pure lead cast (approx. 120 grain) projectiles with some improper dimension RCBS Dies.

I machined .32-20 brass to proper length and rim thickness on a Lathe.

My bullets were not a "Heeled" design. Accuracy was great, but, brass life was short.

My Cases were stretched with head separations after a couple of firings. The case and bullet combination were too close a fit in the chamber throat.
In hindsight, I probably should have just made the cases shorter than the British .310 Cadet dimensions.

"Baltimoreed" - Some of your brass appears to have the appearance of pending "incipient head-separation".