Well I finally bit the bullet, so to speak. After wanting an 1876 for about 10 years I sprung for a new Cimarron / Uberti Centennial with the 28" barrel. I bought the rifle in 45-60 caliber because I was reading that the brass is easily made from 45-70 cases.
Brass...After I ordered the rifle, I started reading about loads. It seems the 45-70 to 40-65 conversion is not as easy as it sounds. The brass differs not only in length, but depending on the headspace in your rifle, you may also have to alter the rim diameter and thickness! I said to heck with it and bought some properly head stamped brass from Jamison. And that required that I buy a shell holder (RCBS #45) to fit it. The brass was here right away and a month before the rifle. Measuring the brass, it came out .010 too short. A minor difference. It also had some nasty burrs around the inside of the flash holes which I uniformed to get rid of those. Later when firing, I also found the brass had shortened another .010" more. All very minor thorns really.
Molds... I then started looking at my molds and their measurements. I had 457191 at 298 gr. and 457192 at 339gr (discontinued) both with no crimp grooves and an RCBS 325-FN. The RCBS had a crimp groove at the perfect nose length for the 1876. All were plain base. I would use the RCBS for non case filling smokeless loads and the 457191 and 457192 molds with black or 777. I also found that Buffalo Arms has a mold which is a copy of the 457191 which has the top lube groove changed to a crimp groove. It is special order and not cheap. All bullets are .457 dia of either 1 in 20 (Black Powder) or 50/50 +2% tin with 5744 and 777.
Rifle...I finally received the rifle and was checking out when I dry fired it and realized the firing pin extension was not bouncing back when I pulled the hammer back. I started to open the lever and the extension jumped right back. I figure that there must be something that wasn't cleaned properly. I took off the side plates and was greeted by a lot of grit. Like fine sand or maybe the remnants of polishing or grinding. I disassembled the entire thing, quite easy actually, and cleaned it all out. There was nothing at all in the firing pin assembly. Leaving the action empty, except for the firing pin assembly, I studied the problem and realized that the extractor was so strong that closing it on an empty chamber would slightly cock the bolt and firing pin and bind them up. Luckily I tried an empty case, with the case in place all was just fine. I still need to work on the trigger which is heavy at almost 9 pounds, but I have now fired the rifle with black, 777 and 5744. The black powder loads are only 51 grains (by weight) of Goex Cartridge and still quite a bit of compression, but accurate. I use the 457192 bullet for these as the lube grooves are bigger that the ones on the 457191. The 777 is not accurate and very dirty. 25gr of 5744 with the RCBS bullet is very accurate and my favorite so far. So far I have only used SPG lube.