Left row, top to bottom:

1. in-game time when the last round is fired
2. whether the gun is chambered or not, 1 = chambered, -1 = not chambered
3. times the guns are cycled, which is equivalent of ammo fired by any one of the guns

Right row, top to bottom:

1. time remaining for the autoloader to be fully loaded
2. whether there's a shell in the breech ready to fire
3. total number of shells fired
4. number of shells in the autoloader

FireGuns: fire guns, the ammo-counting is automatic

FireWeapons: fire cannons, the cannons fire rapidly but if you fire all six shots at once, the cannon would now have a ROF of 1 shot/sec until the autoloader is allowed to replenish.

How to use them:

The Machine Guns:

1. Install a placeholder gun, guide can be seen here. TL;DR: install another gun with activationGroup, damage, lifetime, spread, and impactForce set to "0", bulletScale to "0,0,0", burstCount to "1", roundsPerSecond and timeBetweenBursts to "1e+10", and muzzleVelocity to the same as your gun with the highest muzzle velocity.

2. Create three new variables (or four if you want tracer spacing effects). Set their Expression to "1" as placeholder.

3. Set the Expression of the first variable to
   " FireGuns & ((Time - [first variable name] ) > [actual time between rounds] ) ? Time : [first variable name] "
   This variable records the time when the gun fires.

4. Set the Expression of the second variable to
   " (Time - [first variable name] ) > [actual time between rounds minus at least 0.025] & [third variable name] <= [rounds per gun] "
   This variable defines when the gun is ready to fire; the first condition is when a set amount of time has passed since the previous shot, and the second condition is the gun did not run out of ammunition. Both conditions have to be met for the gun to fire.

5. Set the expression of the third variable to
   " sum(max(rate( [second variable name] ), 0))/2 - 1 "
   This variable records the number of shots fired.

6. (Only if you want tracer spacing effects, otherwise skip this step) Set the Expression of the fourth variable to
   " [second variable name] & (repeat( [third variable name], [tracer spacing]) = 0 | [third variable name] > [rounds per gun minus fifty or so]) "
   This variable defines when a tracer round should be fired; the first condition is that a certain number of rounds had been fired since the last tracer round, and the second condition is the gun is about to be out of ammunition. Either condition would cause the gun to fire a tracer round.

7. Install the actual guns. Set their burstCount to "1", roundPerSecond to something higher than their actual rate of fire, activationGroup to " [second variable name] ", and timeBetweenBursts to something like " [actual time between rounds minus at least 0.025] ". If tracer spacing effects are needed then set the timeBetweenBursts on the gun used to simulate tracers to something like " [actual time between rounds minus at least 0.015] " and the activationGroup to " [fourth variable name] ".
   If the gun(s) require other condition(s) to fire then set the activationGroup to " [second variable name] & [other conditons] " .

The Cannons:

1. Create three new variables. Set their Expression to "1" as placeholder.

2. Set the Expression of the first variable to " smooth(clamp01(rate( [second variable name] )) * [max rounds in the autoloader] , max(rate( [second variable name] ), 1/[time needed for replenish a round into the autoloader] )) "
   This variable records how many rounds need to be loaded into the autoloader/ready-rack.

3. Set the Expression of the second variable to " ammo( "[name of the weapon]" ) > 0 ? [max ammo of the weapon plus 0.1] - ammo( "[name of the weapon]" ) : [second variable name] "
   This variable defines when the gun is ready to fire; either there are still rounds inside the autoloader, or enough time have passed for the autoloader/ready-rack to replenish the first round from the magazine.

4. Set the Expression of the third variable to " floor( [max rounds in the autoloader] - [first variable name] ) "
   This variable records how many rounds are currently inside the autoloader/ready-rack.

5. Install the cannon. Set the activationGroup to " [third variable name] > 0 ", ammoCount to " [maximum ammo of the weapon] ", and firingDelay to " [time needed for the autoloader to reload the gun] ".
   If the cannon(s) require other condition(s) to fire then set the activationGroup to " [third variable name] & [other conditons] " .