You can't take the sky from me
The vast majority of firearms are “electro-kinetic” (EK). These guns are, effectively, miniaturized railguns, using electromagnetic impulses to accelerate small bullets up to lethal speeds.
One advantage of EK guns is that they pretty much all use the same size of ammunition: power is determined primarily by exactly how fast the internal railgun can accelerate the bullet.
Another advantage of EK guns is the standardized reloading mechanism. Unless specified otherwise, all EK guns contain an internal ammo store, and are reloaded via a “hopper” that holds the user’s ammo reserve. To reload, the hopper is attached to the gun, and the gun’s reserve is refilled from the hopper. The same hopper can be used multiple times until depleted.
Reloading from a hopper uses the regular “Reloading” rules on SWD p.49 (free action unless you’re running or doing something else complicated, in which case it counts as a regular action requiring an agility roll (which will probably be subject to multi-action penalty).
EK guns have almost entirely replaced firearms that use chemical-based propellant.
Although commonly referred to as “laser” guns, directed-energy (DE) weapons actually fire bolts of superheated plasma. They do not use physical ammunition, but do eventually overheat (heat capacity measured in shots). Barring environmental factors, any round in which the weapon is not fired, all of its “shots” will be recharged as heat dissipates.
These weapons are rarely used outside of the military, due to their high cost.
“Reloading” a DE weapon doesn’t take any action at all: simply a turn in which the weapon doesn’t fire.