Sounds like you've mismatched sprite numbers. Any sprite form Smoke.pck has 10 frames, not 1, so you need to take that into account when indexing. The first free number is 56, so you should index your first new hit sprite 56, the next 66 etc. Same probably holds true for the explosions, but I haven't tried to modify them myself yet. Try to change the 2nd explosion index from 1 to 8.