Ray,
Sorry I am late to this party. Looks like your chamber is reamed even larger than any fired .303 case I have ever seen. I buy lots of once fired brass when I can find them.
Have you ever made a chamber cast of your chamber?
As far as suggestions go:

1. The 7.65 Mauser can also be use as a neck sizer if you are careful not to set the shoulder back.
2. If your chamber is much larger at the head than a maximum Lee-Enfield chamber you could possible reform other brass if you do not shoot a lot.
Do you have any idea how you headspace is set up? It appears the Canadianicon method for the #4 eventually was the shortest bolt head without going over .074. I ask about the headspace because Hornady .405 Win brass (pricey) has .457 to .458 heads but the rim is a little thicker at .068 to .070. The rim is also a little larger in diameter.
.444 Marlin can also be reformed but it runs a little large than most .303 chambers so it required the head be swaged or reduced slightly.