I bought a SAA, 4 3/4 inch in .44 special, with a spare 44/40 cylinder a few months ago. The barrel is marked ".44 special", and slugs at .429 on the nose. I don't know what the 44/40 specific guns measure at. I did try a box of Black Hills Cowboy 200 grain 44/40's thru the gun, and they shot about 2 inches at 20 yards from a bench rest. You might want to get on the USFA web site and look for a master dealer, as most have a good selection already in stock. You will be impressed with the quality of these revolvers, mine is better then my two Colts.
Larry