Here's an idea on what I think is a good, and a perfectly correct mechanic in operating black powder firearms.
Fouling. Fouling causes musket barrels to become smaller in bore diameter from the powder burning in the cartridge, which causes rounds to get stuck or indefinitely slowing the ramming of the bullet home. Thus the Army later in the war used smaller dies to cast rounds to ease cleaning needs. Example: .570 Minie balls in .580 bores and reducing accuracy.
The idea is, that in (certain) Federal .58 Caliber Minie Ball Arsenal Packs of 10 paper cartridges, 11 caps were provided in a tube, nine .565-.585 Minie ball cartridges and one Williams cleaner round was provided (in various paper colors).
Soldiers were instructed to use these as they did not have a hollow base but a plunger type piston inserted in the bottom of the round and would clear fouling (moderately), until a proper barrel cleaning was performed.
Southerners captured and produced similar cartridges with similar effect.
The Enfield also was able to use these rounds as far as I can recollect.
69 Caliber rounds were avaliable but not purchased from suppliers.
Also, musket cones (nipples if used to this nomenclature) do clog because of residue so a Cone Pick would be nice to implement aswell.
So, in short:
Muskets become unserviceable after a period without cleaning. Either a Cleaner round for certain muskets and rifles, followed by an option to actually clean your barrel with a patch.
Effect: Varying reload speeds with loading cartridges with all muskets from Clean to Dirty to Unservicable and using either a Cleaner round if possibly or physically cleaning with patches (for example, 1842 Springfields). Also, using a Pick of sorts to service the Musket Cone of all Longarms.
If implemented, reloading must be broken down to singular steps of the manual's nine step loading process to either troubleshoot a misfire or cleaning.
Fouling in pistols is far too complex between chain-firing cylinders, misfiring caps, and caps jamming to cause cylinder rotation failure.