[Celjabba]

There is a difference between a small band (which favor close range and effective fire power, so some kind of repeating design is a clear winner) and the OP "army of mook", which call for something economical to manufacture, and cheap to train with.

Either way, making the weapons, assuming you have an example to copy or schematics, is not that difficult as long as you keep to rugged design.
With the right salvage, a steady hand with a file, a lathe, and ideally a trip hammer and a mill to speed things up, you can produce about any 19th century and earlier weapon relatively fast and reliably
Rifling the barrel will need a bit of setup, but nothing truly difficult.

But making metal cartridge, and especially mass producing those, is something else.
Making and loading lots of cartridge is precise work, dangerous work, and require more technical knowledge.

Ence the muzzle-loading (minie ball) flintlock suggestion, or the shotgun / revolver-shotgun.