I would recommend BLACK POWDER ONLY in the conversion cylinders, be them R&D or Kirst. The original gun was marked 'black powder only' and I have no reason to believe that a conversion cylinder changes this.
It even states on Kirst's website, "The cylinders are rated "For Black Powder or equivalent loads only," which includes the current Cowboy Loads on the market."
I have seen these fired with smokeless loads, and have done it myself with reduced loads or special 'cowboy loads', but, I wont try it again, and will stick to BP only with my Kirst Konverters in my Remmie copies.
I also dont really see a reason to use ACP rounds in a replica revolver. I know its been done, and there are cylinders available but, if I wish to shoot ACP, I will buy myself a 1911. If i want to shoot my replicas, then I either use 45LC with BP or 45 Schofield with BP. The Schofield case is shorter than the 45 LC case, and so reduced loads are much easier.
Someone should make a Remington Replica in 44-40...... that would be a definate seller. Problem is that you would need the barrel lined so that it would shoot a 44 bullet without the 'hotdog in the hallway' problem!