I have a custom 45-70 on an Enfield #5 action - Shillen #5 heavy match grade barrel finished @ 20". I load 540 gr hard-cast (Saeco mould) over 44 gr Reloader 7. Chrono said average 1707 ft/sec with SD of 12. Very steamy load but it puts 5 shots into 3/4 " @ 100 meters! Also substantial recoil!
I also have a stainless guide gun, but do not load 540 grainers for it as the Marlin is very fussy about cartridge length and the 540's are a tad long if you crimp in the groove. DO NOT use my listed load in a guide gun as pressures are substantially higher than the gun was designed for.