Howdy
DO NOT REMOVE METAL FROM THE BARREL/CYLINDER GAP UNTIL YOU ARE ABSOLUTELY SURE THAT IS THE PROBLEM!
There is a misconception in the general shooting public that the B/C gap needs to be opened up to shoot Black Powder. This is not true. I shoot Black Powder in single action revolvers all the time. Colts, Rugers, and clones. Every single one of them has the original factory B/C gap that runs between .005 and .008. I have not had to open up a single one of them. The biggest culprit that causes binding when shooting Black Powder in revolvers is insufficient Black Powder compatible bullet lube on the bullets. I noticed you said you are using two groove bullets. In my experience, most of the commercial bullets that are supposed to be used with Black Powder do not carry sufficient lube to be used with Black Powder. Most of them have two skimpy lube grooves on them that do not carry much lube.
Look into the Big Lube bullet designs.
http://www.biglube.com/Default.aspx
The Big Lube bullets were designed specifically to carry enough soft bullet lube to keep the bore lubricated with enough lube to prevent fouling build up in the bore. They also keep the fouling on the surface of the cylinder soft so that it can be easily brushed aside as the cylinder rotates.
The other major cause of binding with Black Powder is an insufficient bushing on the front of the cylinder. Some designs like the Remington 1858 have no bushing on the front of the cylinder and fouling that is blasted out of the B/C gap is deposited directly on the cylinder pin. Once on the cylinder pin the fouling works its way down inside where the cylinder rotates and then it causes binding.
Here is a photo of two cylinders, a 2nd Gen Colt on the right and a Cattleman just like yours on the left. Your Cattleman has a removable bushing just like this. When the bushing is in place, the raised boss at the front of the cylinder shields the cylinder pin from fouling blasted out of the B/C gap. That's why it is there, this design dates back to the Black Powder era.
Get yourself some Ballistol. Apply a light coating of Ballistol to the cylinder pin AND the surface of the bushing, so both are well coated and nice and slippery. Using well designed bullets with plenty of soft Black Powder comparable bullet lube, and the proper design of bushing, you should be able to shoot Black Powder loads with out binding. I do it all the time. Call up Dick Dastardly and ask for a sample of bullets. For 44 Special you will want the 200 grain Mav-Dutchman bullet. I use it in my 44 Russian and 44-40 cartridges. Dick does not sell bullets, he sells molds. But he has links to bullet casters who do cast his bullets.
I recommend against opening up the B/C gap. As I said, ALL of my revolvers have their factory gaps that measure between .005 and .008, and all of them shoot Black Powder just fine. With an unusually tight gap, down around .002 or less, binding can occur, then it is feasible to open up the gap a bit. But most factory gaps are fine just as they are. Opening up the gap can actually make things worse, allowing more fouling than usual to be blasted out of the B/C gap and onto the cylinder pin.
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One other thing. Check the hole where the firing pin pokes through the frame for burrs. If you are seeing scratches on the back surface of your rims, a burr around the hole is the likely culprit, not unburnt powder. Every time the firing pin flashes through the hole in the frame, it rubs against the hole. The firing pin is loose in the hammer and can rotate slightly around the pin that holds it in the hammer. As the pin goes through the hole it 'feels' its way through the hole. That is part of the design. Unfortunately, with the clones, repeated firing can raise a burr at the surface of the hole where the pin emerges and the burr can interfere with the rims of cartridges as they go by. This can be made worse by repeated dry firing.
Colts have a hardened steel insert pressed into the frame to prevent a burr from being raised. Clones do not have this insert and it is very common for a burr to be raised. I bought a used Cimarron Cattleman once that had such a bad burr that I could not turn the cylinder at all with rounds in the chamber. You can remove the burr by filing very carefully with a file held flat against the frame. Just a few strokes is all that is needed. Unfortunately the burr will usually reappear. I have had success by ever so slightly, very carefully counter sinking the hole with the point of a drill. This has to be done very carefully so too much metal is not removed, or things can get even worse, allowing primers to flow into the hole.
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Check out these options before you remove any metal from your B/C gap. Be sure you are using enough soft BP compatible lube such as SPG on your bullets. Your concoction should be fine, you may need more. Be sure your bushing and cylinder pin are well lubed. And check for burrs around the firing pin hole.