I have been shooting my 1886 Springfield (Trapdoor) for years using 300gr JHP's and IMR 4895 without a hitch. I decided to try a BP sub, Pyrodex P,and a 405 gr Moyer cast bullet .459 dia and loaded with 70gr by volume with milk carton wad. The 1st three shots touched, range was 100 yds so I was really impressed with a sub MOA group from a 125 year old gun. Tried a few more shots and they started to spread with shots 8,9 and 10 keyholing through the target. Am I going to have to clean the bore every three shots or is there other problems ?