Tried out the pistol again last night with some better results. The .457 balls fit much better into the chambers but they still looked to be shooting the same as the .454 (roughly). So again all my rounds were going into the bottom target not the top one I was aiming at. I decided to increase my powder load from the 15 grains, to what im not sure because the nozzle isnt marked but it was inbetween the 15 and 30 so maybe 20 or 25, this produced better results the rounds were going higher and I was getting more of a grouping around the middle of the two targets.

Since they were grouping around the middle i started aiming at the top of the target I was trying to hit, I found this difficult with there not being a clear point to aim at but I got some reasonable results, didnt get the black but came close. So next time I think I will mark the top of the target with something to give me an aiming point and see how it goes.