I agree with Jon F, that you should use .38-55 brass. I think the bullet diameter you were using was a bit large for a modern barrel. I have a Chief Crazy Horse that I use .375 cast bullets in. I also have used the Barnes jacketed bullets and had good success. They are .377, if I remember correctly. I think that you will find that cast bullets are all you need for deer or black bear. THe factory ammo is way underloaded, and it feels like shooting an overgrown .22 Magnum.