I’ve owned seven different rifles in 45-70 and had one Encore barrel in 45-70. I’ve been reloading for around fifty years now and I have to say that the 45-70 is the least fussy cartridge I’ve ever loaded for. Here’s my absolutely best advice I can give to you based on what your stated expections/purpose are. Get a Lyman reloading manual, look at all the loads under the section dedicated to Trapdoor loads (the least powerful loads) and pick any powder listed for the bullet you want to shoot. Based on my experience, you’ll probably be satisfied with any of the loads offered. One minor suggestion I can make based on my experience, choose a heavier bullet than the 300 grain. Every gun I own or have owned shot the best group with heavier bullets…..400g, or at least 350g. They’re still quite manageable at Trapdoor levels. Every deer I have shot with these loads has been complete pass through on deer regardless of distance or angle. If you’re new at this, please read the book on how to do it and get some mentoring if possible. Don’t use any loads that are not in the reloading manual. It can be dangerous to do so. Lots of bad advice out there. Good luck.