Secret to shooting round balls in those is to be sure it is super tight patch and drop the powder charge down to a minimum and work up. You never will get very high, probably not enough for big game but may be enough for fun and small game.

It strips the patch through the rifling with too much bang.

If I wanted to save and still hunt with it, I'd start looking to hard cast bullets and work up from a minimum until they start stripping instead of spinning. May be able to make a satisfactory velocity that way.

You could always use cast bullets to fit sabots for the gun and shoot cast that way instead of jacketed. Those should match the copper jacket weight bullets exactly in about every way and be able to shoot them just as hard.