I have the convertible Blackhawk, and have not found accuracy to vary between the Colt vs. ACP loads...........but, so far all I have have shot have been 200 grain lswc bullets at around 950 fps out of both cartridges, so I don't really have a lot to go on.
The ACP loads are my standard reloads, and I did not realize when I loaded the Colts that although its different powder and charge weight, they were the same velocity.