I suggest you do as you see fit .
Now here's what I've done over the past dozen or so years in this application .
My first try with the 45-70 was a MArlin 1895CB with the 26” ballard rifled barrel . And I used the Lee 457-340 PB and the Lee 457-405PB with pretty decent results pushing them with SR4759 . After awhile I went to the Lyman 330 grain Gould HP PB bullet again pushed with SR4759 . In all three cases I used aircooled wheelweight alloy NOTHING added . The Gould bullet pushed with SR4759 in the 1895CB I had was a deer killer PERIOD .
After that I went to XMP5744 because as someone already mentioned it was less position sensitive then SR4759 . But by then I had also moved on the the two Ranch Dog gas check bullets . With the Ranch Dog 460-350GC and a good load of XMP5744 I knocked over the best racked whitetail I've taken in 40+ years of hunting . The shot was about 60 yards and again I was using aircooled wheelweights in a circa 1978 Marlin 1895 with Micro Groove rifling . Later that same year I used the Ranch Dog 460-425GC in a Marlin 1895G with ballard rifling and air cooled again . Hit a spike at about 12 yards and hammered him straight to the ground , of course I was about 30 feet above him sitting in a climbimg treestand .
When I started using H322 in the 45-70 loads I needed to water quench to get the bullets to stop stripping in the Micro Groove barrel . My present circa 1972 Marlin 1895 is one of the first from that year and isn't Micro Groove but I decided to keep water quenching anyway .
At the moment I am using H322 with all three of the Ranch Dog 45 cal bullets as well as the BRP 462-465GC and the BallistiCast 462-550GC and they all shoot well enough at 100 yards for deer hunting .
I'm however in the midst of possibly changing over with the Ranch Dog 460-300GC to shooting VV N-120 powder . This stuff showed some pretty good results the last time I was at the range and it doesn't seem to be loosing anything velocity wise to the H322 load I've been shooting for a couple months .
Oh yeah I almost forgot !
I have an original 1884 Trapdoor that someone saw fit to cut down and try to make an artillery model out of . Gun still has original case coloring on the lock hammer etc . Anyway I shoot the Lyman 388 grain RN PB bullet in that one with SR4759 at maybe barely sonic velocity . Gun shoots okay at 50 yards using the original sights . While some folks like BP I ain't exactly one of them except in my old original 1840's half stock Pennsylvania “A.B.Smith” percussion rifle . Closed action cartridge guns ain't no place for BP if I own them .
Dale53 , on a side note I finally got my “System Grothe” 8.15x46R schuetzen rifle going !
If you happen to come to Brushy Mountain Gun Club to shoot in the Chinkapin Shoot let me know I'll try and drive down to finally meet you . I assume your buddy is going to hold them again this year .