I'm very new to black powder reloading, but very much not new to metallic cartridge reloading having loaded in the neighborhood of 50k smokeless rounds in various modern calibers. I'm restoring a 1866 Springfield 2nd Allin conversion in 50-70. I read most everything I could find, bought 20 cases, some Goex FFg, a wad cutter, and some bullet lube. Also purchased a furnace and some soft lead ingots. Slugging the barrel after extensive lead removal yielded a bore of .518" across the groves. It turns out, the Lyman mold I bought drops 450 grain bullets at that very diameter, so no sizing required. For my first try. I loaded five rounds with 65 grains of FFg (to err on the safe side), a .050" paper wad with two newsprint wads under the bullet. Powder was dropped through a drop tube, and then compressed .090" before bullet seating and crimp. The first shot, although highly anxious, fired normally without blowing anything up. It took the other four shots to hit the paper at 100 yards after finding it was shooting about 18" high. I subsequently loaded twenty more, and had a fine time blasting away at the bottom of the target frame to hit somewhere on the target.
I have now loaded twenty more rounds using the same procedure, but with 60 grains of FFg. Here is my question: am I doing anything dangerous by going with five grains less powder? I know, seems like a dumb question, but I very much want the bullet to exit the barrel in the normal fashion without damaging me nor the gun.
The rifle I'm restoring had been sporterized at some point in its history, although thankfully they left the barrel the length it was born with. They shortened the stock to a single band, but did a nice job of it, even replacing the end cap. They also blued the barrel and did an exceptional job of it. I suspect they might have filed down the front sight post to make it a 200 or 300 yard gun, since it shoots so high at 100 yards with a reduced (65g) load. Why they wouldn't just flip the rear sight up is anyone's guess.
If I can't load my way onto the paper at 100 yards, I will likely try to add a bit to the front sight post (braze or weld tbd).