Yes .530-.535 ball size depending upon the bore size, powder fouling, lube etc. if using a .535 ball and it starts loading hard then I would switch to .530 accuracy was not diminished.
I have been using alox for years in smoothbores with good success.
These are fun to shoot. I use premeasued charges in soft tubes with the ball stuck in the end which makes it quick and easy. If your pistol uses a #11 cap I would change it to use a musket cap for sure ignition. I have had the smaller nipples plug up badly but eliminated the problem with musket caps.