I'd be surprised if your 1858 held 50 grains of 3Fg. Not unless you had it specially modified. From what I recall, 35 grains would be pretty much a full load and that may be generous. In any event, just make sure your ball sits firmly on your powder. If you feel the need to get the ball closer to the forcing cone then you can experiment by adding a little corn meal, grits, cream-of-wheat, et al until the ball sits where you want it. Or add a lubricated wad.