1) if you have a Buffalo Classic, your bore is likely .457. Most of them are. Slug it anyway if you like. I would, but these rifles seem to shoot better with slugs sized .458 or .459. I'm not sure why but that seems to be the consensus on the forums. Likely the standard Handi 45-70 is the same. I'm sure someone here knows for sure.
2) I like the NEI moulds of with big meplats in several weights. You may as well go ahead and get gas checked designs. Eventually you'll likely want to up your velocity some and the gaschecked bullets do at least as well as the non gaschecked ones at the lower velocities. I've also bought a Lyman 457122 and it drops at barely .457. Not the .458 -.459 that they claim; I have a Lee similar to the 459-405-HB except it is HP instead of HB and it does the same as the Lyman. Drops the bullets at barely .457 rather than the .459 claimed. This has been the case with both soft and hard alloys. It would seem that you are gambling in selecting these moulds but mine may be exceptions.
3) My favorite powder for the type loads you are projecting you want is Accurate XMR 5744. ie for velocities from 1200 to 1600 fps with 350 - 450 gr bullets. For a little more velocity for hunting or whatever, try Reloader 7, Varget, or 3031. They've all done well for me.
4) Any standard large rifle primer will do good for you. I like the CCI BenchRest Primers, but there's little difference in results with others I've tried. For bigger charges of Varget, I have found Federal mag LRP's give more consistent mvl's when using heavier (recommended) charges and visually more efficient burning. (ie fewer unburned powder granules).
5) I like the 350 gr and 405 -430 gr weights best. If you do have a mould that cast undersized, these do a little better if not cast too hard. Just plain wheelweights with a little tin to improve castability is likely your best all around for 1300 - 1600 fps and, if you are using gas checks (strongly recommended unless you're just a die hard traditionalist), you can push this alloy even faster with accuracy and without leading. I size and lube mine in my old Lyman 450's with home made Felix lube, but any commercial lube will likely do very well for you.
Good luck and happy shooting. I know what you mean about "thunking" LOL . I like that term. I bet it catches on
Best Regards,
stuffit
Oh! on the powder charges of the powders I've mentioned, PM me if you'd like numbers on some of the one's I've used and how they did.
s.
