PC
I've never shot enough gas checked cast bullets though my 45-70s to answer your question about barrel wear. I've shot thousands maybe tens of thousands cast bullets through my 45-70s with gas checked bullets with no noticable effect on the barrel.
I shoot nothing but gas checked cast bullets, all home made and I use the loads made for the Marlins. I've not found any leading, the accuracy was as perfect as the shooter could allow.
I'd suggest you find gas checked or non gas checked in .458 to .460 diameter, with a good hard lube, using a moderately hard alloy.
Give the gas checked bullets a try and I doubt you'll bother with the non gas checked.
Jim