Gear and Methods of the Matchlock Rifleman. Not as dry as my title, this video has a fellow going over the process of loading and firing a matchlock rifle. Also displays period garb, armor, equipment. Folk were apparently taught to load without putting the rifle on the ground, so they could load on the move, which seems totally bananas to me. Also, putting a lit match near the black powder that touches off your rifle presents some obvious safety concerns. It's easy to see why a flintlock or wheel lock was considered a step up in technology - the wheel lock being the step that overcomplicated things too much, but got away from 'lit match juggle reload,' the flintlock as the step which resolved the mechanical complexity.
It's neat to see in the above example, the re-enactor is wearing a plate male cuirass. Probably wouldn't help much against bullets, but who knows. The capandball YouTube channel has a video about shooting lamellar armor with these kinds of guns.
Match lock rifles firing line - it would suck to juggle gunpowder and a lit piece of string like that. Gunpowder out in the air won't explode like TNT or C4 or the like - it burns and burns really fast. But still, you could spill and get a nasty powder burn or the like. You can see the fellow at the end with his Apostles, seemingly running through faster thanks to them.
Wheel Lock Carbine - loading, firing. Really cool mechanism. Especially the way the flint is basically lowered into the front of this trough filled with black powder, and the spring-wound wheel spins around, rubbing itself against the flint, flinging sparks into the powder pan.
Wheel Lock Rifle - short, slow motion.
Flintlock rifle loading and firing - looks like this one has a rifled barrel, too. Probably too advanced for OSR games, but it's not like I've ever seen rules for rifled barrels. Practically, those make shots more accurate, especially over distance.
There are actually a lot of flintlock videos on youtube; if you want more, find some!
The paid version of Lamentations of the Flame Princess (the rulebook) contains an appendix section on firearms that largely goes over these points. It's nice to have some video references, especially on how the wheel lock works. It also specifically mentions the kind of armor you see in that first video.