Mike - I have been making these cases from Hornady .405 Win with no issues. They need trimming to length, and the rim diameter has to be reduced, as does the thickness (I make it suit my rifle). The Hornady brass is a little thicker than Bertram, and yields a minimal clearance in my rifle's chamber.
I'm not sure what is the cause of the case crushing, I use a .373 expander also, and the Hornady jacketed bullets seat with no trouble. I flare the case mouth to seat cast bullets.
My rifle looks like it was made in the same batch as the one you have, except it has the 320 grain proof. She is a shooter!
Is your barrel left hand twist?
PM me if you'd like to see my loads.
