I'm just thinking here, but wouldn't most belted magnum snap caps work? Won't a Lott will fire .458 Win. Mag catridges? That's the same case as a .264 Win., 7mm Rem. Mag, .338 Win. Mag.. I think its awfully close to .300 and .358 Norma Mags as well.
Anyway, just trying to help. Best of luck...