Howdy Bruce,
I have the same gun, one of the first 44 spcl '66's imported in 2000. I have shot a lot of APP, 777, and BP in it. I tried the 777 with a 254 gr bullet and neck-sized-only brass in an attempt to find a load hot enough to expand the brass to seal the chamber to minimize fouling in the action. It didn't help
. The only thing I didn't try was annealing the brass. Might be the Uberti .44 spcl chambers are generous, I don't know. So, I just give the carrier a spritz of either moosemilk or plain water if it gets sticky in the middle of the match, no big deal. .44 Spcl is a fine cartridge, easy to load and accurate. While BP gives a nice patina to the brass frame if left unpolished, I will say that both APP and 777 will stain the brass in spots, so be sure to wipe it off good ASAP after shooting, or even in the middle of a match, or live with the stains. I used to polish it once a year or so, but nowadays try to stick with real BP for the smokey stuff and let it patina. The oil you use to lube the carrier area when you clean it will keep any fouling inside the action neutralized so it won't hurt the innards, although it will get goopy in there.