RE: Type of Powder?
Right the " in" powder is Triple 7. Try in a 2fg cut and, if you have a load worked out reduce it by about 10 grains, simply becuase T7 is hotter than the other powders. T7 cleans up easy and seems to be very consitant. Disadvantage is cost. You will pay more for this powder.
I love shooting real black powder, but only do it in my traditional styled guns, BP' s only advantage is its low ignition point, but the other powders are very reliable even with a no. 11 caps, so ignition problems usually are not the fault of the powder. Clean up is not hard, but BP produces a lot of fouling, and is VERY corrosive even in stainless steel barrels.
Pyrodex, is a proven substitute, and in my opinion is very similar to BP. It produces a lot fouling and is also corrosive, but less than BP.
I would start with T7 or Pyrodex in your gun. Either will work great, and going with loose powder will let you work up the perfect load.