Howdy
A few things about the Remington 1858 New Model Army and its replicas.
This is my old EuroArms Remmie I bought brand spanky new in 1975. It is actually fitted with a cartridge conversion cylinder in this photo, but I will get into that later.
The 1858 Remington had a design defect. The cylinder was (is) flat across the front. At left is a cartridge conversion cylinder, at the right is the original Cap & Ball cylinder.
What this means is that Black Powder fouling that gets blasted out of the barrel cylinder gap gets deposited directly onto the cylinder pin.
Because the cylinder pin is so thin, only about 1/4" in diameter, fouling deposited on the pin builds up rapidly, and as it works its way between the pin and the cylinder the fouling causes the cylinder to bind.
In this photo you can see how thin the Remington cylinder pin is. Also in this photo is a replica of the 1860 Colt Army. Notice it too has a flat cylinder face, so again there is nothing preventing fouling from building up on the cylinder arbor. But notice how much larger in diameter the Colt arbor is than the Remington pin. This means that for every shot fired out of the Colt, there is more surface area for the fouling to be distributed over. Notice too the helical groove running around the Colt arbor. The groove provides clearance for fouling to build up in, so the Colt can be fired for more shots than the Remington without binding.
Now let's look at how Colt solved this problem with the 1873 Single Action Army. Left to right, the three cylinders in this photo are from an Uberti Cattleman, a modern Ruger Vaquero, and a 2nd Generation Colt SAA. Notice the fronts of the cylinders are not flat. They each have a bushing on them. The bushings on the Uberti and the Colt are removable, the bushing on the Ruger is not, but that does not matter. The point is, each has a bushing that extends out in front of the cylinder face.
Here is a close up of the cylinder barrel gap on a Colt. Notice the barrel extends back to within a few thousandths of an inch of the front face of the cylinder. But the front end of the cylinder bushing is projecting out past the barrel/cylinder gap.
You can see it even more plainly on this Stainless Ruger Vaquero. When Black Powder fouling is blasted out of the barrel/cylinder gap, the horizontal separation between the gap and the front of the bushing prevents fouling from being blasted onto the cylinder pin. The bushing shields it.
I shoot Black Powder in cartridges in my Colts at Cowboy Action matches all the time. I can shoot six stages of a match, 30 rounds through each revolver, without giving my revolvers any attention at all. They just keep on shooting without binding. In fact, I can easily fire 50 Black Powder rounds, probably more, through my Colts without any binding at all.
In contrast, when shooting Black Powder cartridges in the conversion cylinders of my Remingtons, I have to pop out the cylinder after every five rounds to wipe fouling off the front of the cylinder and the cylinder pin, or they will begin to bind up. In truth, this is not a problem with the Remingtons because their design makes it very simple to pop out the cylinder for cleaning. With Colt type Cap & Ball replicas, you have to drive out the wedge and pull the barrel to clean the cylinder. Much easier with the Remington design.
There is actually a fair amount more detail to loading Black Powder in cartridges, but that is a topic for another post.
If you want a Remmie, go for it. Just be prepared to wipe off the cylinder fairly often.
Regarding cartridge conversion cylinders, they are made of better steel than the typical Cap & Ball cylinder that comes with a Cap & Ball cylinder. They are proofed for Smokeless loads. Of course, you cannot put loads more powerful than SAAMI spec loads in them, but you should not do that in a Colt or Uberti either. Yes, if you want to fire cartridges in a Remington with a cartridge conversion cylinder, you must buy a steel framed revolver, not a brass framed one. The manufacturers of conversion cylinders state this quite plainly.
Regarding real Black Powder vs the substitutes, I must admit that all of my experience is with real Black Powder, not the substitutes. You might be surprised how easy it actually is to clean a revolver that has been fired with Black Powder. It is not as difficult as you may think. Yes, it is messy, but it is not difficult.
And I never completely disassemble my revolvers after firing them with Black Powder. I have treated the insides so all I have to do is clean the bore, chambers, and the outside surfaces. I have developed some techniques that prevent fouling that makes its way down inside from causing corrosion.
If you want a more detailed description of loading Black Powder in cartridges see here:
https://www.thehighroad.org/index.php?threads/shooting-black-powder-in-cartridge-guns.821193/
That thread is not completed yet, I need to get back to it and finish up BP cleanup, loading BP in shotgun shells, and BP cartridge loading for single shot rifles. But it is a good place to get started.