ZEITGEIST Muzzle-loading property


In the "Keep your powder dry" and ZEITGEIST 5E rules, most firearms have the muzzle-loading property: "Because of the extreme times required to reload this weapon, you must spend an action or bonus action to reload before you can shoot again".

I am a bit confused about the "bonus action" part of this. Does every character and NPC who is proficient with those firearms have the ability to spend a bonus action to reload? In other words, is the only disadvantage of a muzzle-loading firearm that you can't spend your bonus action on something else? Can somebody proficient with a musket shoot every turn? If he has two attacks, can he shoot, reload as bonus action and shoot again in the first turn?

The alternative would be that one needs a special ability that allows you to spend a bonus action in order to use it to reload. Characters without that ability (thus all player characters) can only shoot a muzzle-loading firearm every second round.

Which one is it?
In 5e we intentionally changed it so yes, if you have two attacks you can fire and reload and fire again. But the next round you have to use a bonus action to relax before firing once.

Guns in 4e were better than they are in 5e, sure to how attack powers would let you use multiple dice.
Anyway at least in the pathfinder version Breech loading rifles and revolvers are available as early as book 3 , as well as Nock Guns