....SPG Lubricants BP Reloading Primer.
I am much disappointed to see that the .44-40 is absent from the list of cartridges discussed in the book.
Still I am pretty happy wif it.
Haven't slugged the bore yet.
I bought some Cowboy loads at the last gunshow and the slugs measure .426. Surprisingly smallish.
I'm going to suggest you try the Big Lube Mav-Dutchman 200 grain bullet in your 44-40 loads if you are going to be shooting Black Powder. My experience with other bullets, even the ones that stated they were for Black Powder, is that they did not carry enough lube to keep the bore lubed its entire length. Most 'BP' bullets are fine in revolvers, however most run out of lube about 6" before the muzzle, causing the fouling in the last 6" of the barrel to turn hard and crusty. This in turn ruins accuracy. Easy enough to fix by swabbing the bore a couple of times with your favorite water based BP solvent, but if you don't want to be swabbing the bore to maintain accuracy, the Big Lube family of bullets are the ticket. They carry a ton of BP lube. You want to see a nice Lube Star at the muzzle, indicating that the bullet still had some lube in it when it left the muzzle.
No sweat about 44-40 not being on the SPG website. Just use whatever bullet carries the most SPG you can get into the lube groove and use enough FFg (or FFFg) so that when you seat the bullet the powder is compressed by 1/16" to 1/8". That's all there is to it. No need for card wads or anything else, just compress the powder with the bullet. My standard BP 44-40 load is the aforementioned Mav-Dutchman bullet sized to .428 and lubed with SPG, seated over 2.2CC of FFg. I usually use Schuetzen, but any FFg will do. Don't use a heaping dipper full, scrape the dipper level at the top.
Regarding polishing the frame, if I owned a brass framed rifle, which I don't, I would not bother polishing it. BP fouling will bring a very pleasing patina to the brass in a short time.