I highly recommend slugging your bore to see what size it is. Then buy the appropriate size bullets for the bore. If you haven't done so, you might want to check out Beartooth Bullets . Marshall Stanton has put together a great guide for understanding cast bullet shooting. His book "Beartooth Technical Guide" is outstanding and nicely priced. You also will not find better cast bullets anywhere than his, but they aren't cheap, and worth every penny.