RWS makes good caps. However, as stated in my post above, the CCI Reenactment caps worked for me, the last time I had my 1842 at the range. I believe I was shooting Goex FFg.
It's just that the general consensus seems to be that the CCI Reenactment caps are not as hot as the regular old CCI caps were back in the day, and not as hot as some of the others that may be available. I suppose that could be an issue, depending on the type of nipple and/or propellant.
I would recommend that you visit the N-SSA website and forum, and ask what brand of caps those people like best. I don't know where you live, but another additional thing to try (under normal conditions) might be to look for Civil War reenactments or encampments within driving distance. Events this year are probably cancelled due to the pandemic. Anyway, they usually have sutlers at those events who can sell you small quantities of caps on site, so you don't have to pay shipping or HazMat fees. Find what works, then order in quantity.
If it were me, I would take a chance and order a thousand of the RWS (which I did, a few years ago), or the Scheutzen caps (which I have not tried, but I would take a chance on 'em if I needed caps) in addition to one or two tins of the CCI caps. Or, buy two or three tins of all three, if you can get them all from one vendor at the same time to save on shipping and HazMat. Try them out and see what you think. If the CCIs are hot enough, that's good, because they seem to be the easiest to get, generally speaking.
As a final suggestion... Since we are all friends here... I would suggest you look up Smokey Plainsman, send him a private message and ask him what kind of caps he was using when he shot that big old horse pistol of his. He posted about a successful day of shooting with that beast recently, and I'm pretty sure his pistol uses musket caps. He didn't report any problems.
Best of luck to you!
Notchy Bob