A couple things I'd like to add, would be to make sure to keep the good quality files in a dry place, and only use them for bullet knurling. Use a file cleaner, and a good quality rust preventative on them. You do not want any rust particles or metal shavings getting imbedded into your bullets while knurling. That would not be good for your bore.
When Hank says keep your barrels dirty, he is talking about them exotic powders that are not approved for "black powder rifles". You mentioned you wanted to use Blackhorn 209, so keep them clean after each shooting session, unless you happen to be carrying one of those golden horseshoe suppositories around.
Make sure you have a good ignition source with a locking bolt, standing breech, or locking breech block.
Sometimes a guy gets lucky, and can find certain bullets to fit certain bores, but not something you can count on without having several rifles and trying several bullets.
The smooth sizing dies would be the way to go, to get the perfect fit for several different bullets and bore sizes.
Use a wad between your bullet and powder. Sagebrush makes the largest diameter 0.462" and 0.518" veggie wads in both 0.030" and 0.060" thick. If you go with wool wads, use .50 cal wads in the .45 cals, and use .54 cal wads in the .50 cals.
https://m.sageoutfitters.com/catalog/item/7209324/7463753.htm
Start with moderate powder loads, and work up only in rifles suited for shooting sabotless with Blackhorn 209. Depending on breech plug design, and brand of 209 primer, they can be all over the map as far as visible pressure signs. Just keep your loads under the maximum published loads on Western Powders Load Data for the bullet weight you are shooting. There is no published technical Load Data for .45 caliber rifles, or any other caliber besides .50 caliber. So keep that in mind.
The best, easiest bullets to get to shoot sabotless are lead core, copper jacketed bullets. Monolithic copper or brass bullets are damn hard to get to obturate into the grooves enough to stabilize with Blackhorn 209 in my experience. So much so, that I have discounted them as viable options.
"Keep your stick on the ice"!