I did it. Once.
I'm assuming that you're talking .30-30. I filled a few cases up a bit short of the mouth, maybe an eighth of an inch, then seated the bullet to compress the powder and used a fairly heavy crimp (I wasn't sure just how hard that powder was pushing back).
The net result was a very dirty gun because the bullets that I used did not have the deep grease grooves that a BP bullet should have, so the fouling built up pretty quickly.
I do have a '94 in .32WS and some bullets that have deep grooves, but the rifle is just ill-suited to shooting black powder (in my opinion) because it's just too hard to clean out any gunk that gets back into the receiver.
I've read that right around the time that the .30-30 was introduced, at the tail end of the black powder era, that black powder was cleaner burning than the stuff we use today, more like Swiss powder than any of the others. I don't know if that's true or not - I was using Pyrodex for my "experiment".
Anyway, if you're going to give it a try, just fill up the case. You're not going to overcharge the round, no matter how much BP you put in there.