Yeah, mine was a little off also. I took a diamond burr that was flat on the bottom and slightly changed the angle. I did find however, that the nipple went too far into the drum. I had a lot of misfires.
I removed the side cleanout screw, and replaced it with an Allen head scres that went to the nipple. This closed off the chamber to only one side. At least, one side had direct firing pressure. I also ground off one thread on the nipple. Still all the threads going into the drum, but none touching the other side. With the slight grinding, changing the cleanout screw, and removing a little of the nipple, Reliable firing.
I had also found, a piece of cap jammed into the well on the hammer, making hammerfal ang up. The hammer went a little lower, so I reshaped the nipple just a bit.
My wife loves the rifle, when we go to the range, and we do some serious charges with it. A nice little rifle/wall hanger. We restocked it with an one piece, I made some sights that were more period, did some dovetailing, and there she be.
A nice little one shot. We used brass Hawken furniture. Looks better with the original lines on the rifle.