I have a RRA 16" 458 socom. I handload Barnes TTX bullets to hunt with. I never tried using the standard 45/70 jhp rounds that will fit in the case, so i dont know about those.
i have not modified nor have i used special magazines for the rounds.
I use 30rd PMAGS and CMMG 10rd magazines. No problems.
super expensive to shoot. i hope you reload. dont lose your brass, they're ~$2/each.
PLAN PLAN PLAN
A prudent man forsees evil and hides himself; the simple pass on and are punished