I agree with Pettifogger, get the Wolf book. However, he designed a bullet that Lee makes a mold for, it is a 405 grain hollow base that usually drops from the mold around .457 - .459, depending on the lead. Go soft with the lead. I use blackpowder lube on them and load and shoot them unsized over a compressed load of 2F BP. However, Wolf also used the same bullet with smokeless. I also have an original Winchester mold that makes a 500 grain bullet that I cast with soft (pure) lead and load unsized. I think the soft lead "bumps up" to engage the rifling. I've hit 12" tall buffalo plates at 100 yards with 1873 sights. Your '84 should have a little better iron sights.
I'd give you more info but I haven't seen my book in years, but it has more info than you'll ever want to slog through. I didn't do everything Wolf said to do but still got greatly improved accuracy over my earlier attempts.