My Kangaroo Rifle is a BSA in .32-20ish. I use unaltered new .32-20 brass reloaded with .30 carbine dies. A real sweetheart to shoot.

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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".

What pressures were you reaching with your loads to get the case separations?

I do not believe the pressures were high or the cause of the case separations.

I was using reasonable loads of IMR-4227 in a straight walled case.

I think the problem was caused by the case mouth being unable to expand to the side and being stretched forward by its grip on the bullet in the tight confines of the chamber throat.

BTW - My B.S.A. .310 Cadet Martini's bore diameter measured .317".
The chamber was original, not modified.

(IIRC - Kynoch factory ammo used a 'Heeled' projectile with an approximate base area diameter of .310". The exposed section of the bullet, in front of the case mouth, measured about .318").

I mention these details because some of Baltimoreed's brass has similar looking 'stretch' marks, (where the wall meets the web) to my brass that separated.

Some of my brass has a ridge while others don’t but I’m wondering if its from the sizing die. [The ones without the ridge might be a first loading.] My load is only 3.0 gr of Bullseye with 130 and 150 gr lead. I don’t think I’ve shot it enough to work the brass. Here’s what my cerrosafe cast looked like. It’s got an odd chamber, not a .310 or .32-20. The 32-20 shoulder blow out and you get a straight wall case. How long should the brass be?

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Nice shooting! What diameter bullet?

.321 150 gr from Western Bullet Co.