1873 springfield trapdoor
my brother recently bought a trapdoor springfield. i have a few questions about loading for this gun. We quickliy realised that they have a battle sight set up for 250 yards, so he replaced the front sight for a larger one and got it sighted in 1" high at 50 yards using factory loaded blackpowder cartridges with a 405 gr. lead bullet. i loaded 3 loads out of the fifth edition hornady manual using there suggested 300 grain jacketed bullet. He said that the gun had far more recoil with the black powder cartridges than it did with he hornady 300 gr hp and 409 grs of imr 3031 ( the starting load from the manual )
question 1: it is suggested to keep the loads under 29000 psi, the manual says the loads are under 28000 c.u.p. how do p.s.i and c.u.p differ?
question 2: are modern jacketed bullets to hard for the rifling, and if so, are there any suggestions for what bullet, or loads, to use safely? i was looking for an alternative to lead just for a cleaner bore.
question 3: Is there a more specific loading manual for antique/ collectible firearms that may be better suited for loading for the trapdoor?
i know i can do research on the internet, but would prefer first hand experience and knowledge pertaining to this particular firearm.
I certainly dont want to damage it in any way shape or form.