Make sure you don't use a modern black powder substitute or your Colt will be destroyed.
Ummm, yeah, OK...
Now for the real story. Pre-WWII (or Pre-war) SAA's do indeed have a groove diameter of .454". Post-WWII (or Post-war) SAA's have a groove diameter of .451". This was because after WWII there was lots of tooling to build .45 ACP barrels, and the .45 Colt tooling was just plain worn out. So rather than spend money on new tooling, the stuff in use was used to make .45 Colt barrels and the specs were changed.
Now according to load data listed in Mike Veturino's book "Shooting Sixguns of the Old West" were as follows. Page 171 BTW.
Colt SAA 4 3/4" vintage 1892
NEI mould #454-255PB 1:20 alloy sized .454" weighing 252 grains
CCI-350 Large Pistol Magnums
Starline brass
35.0 gr FFg............ 808 fps
35.0 gr FFFg.......... 870 fps
35.0 gr Ctg............ 747 fps
25.0 gr Pyrodex P.... 869fps And last I talked to Mike, he still has all of his extremidies and digits, so I gather he didn't have a gun blow up on him.
When it comes to BP cleanup, I find it easier to use Windex with Vinegar, and Ballistol for a final coating. The brass is de-primed and soaked in hot-as-I-can-get soapy water and then tumbled in ceramic media. If you need help loading BP, just ask. I looked back on your posts, and see you're one of them there nitro powder types.

Be glad to help. There's more to it than you would think.
Congratulations on getting a 1st generation shooter. Afraid that other than Ten-X BP factory loads, handloading is your only option. And for what Ten-X would cost, it wouldn't take long to break even. Just for the love of Pete, don't use smokeless. Some internet commandos might swear you can, but there is a guy out there (a friend of Mike V's as it happens) named Kirk Stovall. Mike has bestowed the alias of "Shrapnel" upon him... care to hazard a guess as to how he got that one?