Howdy
Dunno if you fired the gun yet, but if it was mine I would only load it with Black Powder. Or a substitute. Your uncle may not want to mess with Black Powder, but does he want the gun to blow up? APP is a good substitute and does not require specially lubed bullets the way real Black Powder does.
Yes, loading 44-40 is a bit fussy, but I have loaded thousands of rounds, most of them with Black Powder. You just have to set your dies very carefully, and not bang the cases into the bottom of the die.