I've been having a number of issues with beam weapons on fighters...
I wanted to make an anti-shield beam cannon, but it seemed to do damage to fighter hulls even with an armor multiplier of 0. So I changed that away and decided to live with it.
However, I also tried to make a close-assault beam cannon and have run into a different problem. When I hold down fire, the beam cannon seems to continue firing at one shot a second or so regardless of the specified firewait value. This is a bit of a problem; the concept was the beam cannon would do a ton of front-loaded damage against capital ships and perhaps bombers, accomplished successfully through the use of armor tables to selectively multiply the damage against capital ship armor. While it was firing, it would essentially gobble up most or all of a fighter's energy, so you'd pull up to come around for another pass. Since the firewait tag isn't working, the AI just sits there firing it for a microsecond over and over not accomplishing much. Furthermore the effects seem to pile up on top of each other a bit.
So I decided to try to up the warmdown time to 9000, except that doesn't work either; that only happens after you pull the trigger and its fired as many shots as you are able. I added the "ballistic" tag, to represent additional battery packs or something fueling this neato gun. The ammunition supply displays correctly, but none is used up when I squeezed the trigger (which is odd, as I assumed it would happen at the same rate as energy was drained).
I'm using FS2_open_3_6_12r_INF.exe and here's the relevant portion of the weapon:
$Mass: 0.015
$Velocity: 2000.0
$Fire Wait: 9.0
$Damage: 2
$Damage Type: Quantum
$Armor Factor: 1.0
$Shield Factor: 0.25
$Subsystem Factor: 5.0
$Lifetime: 5.0
$Energy Consumed: 0.0
$Cargo Size: 1.0
$Homing: NO
$LaunchSnd: -1
$ImpactSnd: 85
$Rearm Rate: 100
+Weapon Range: 800
$Flags: ( "player allowed" "in tech database" "beam" "no pierce shields" "ballistic" )
$Icon: iconNewton
$Anim: Newton
$Impact Explosion: BlueBeamGlow2
$Impact Explosion Radius: 3.0
$BeamInfo:
+Type: 0
+Life: 3
+Warmup: 1000
+Warmdown: 7000
+Radius: 1
+PCount: 0
+PRadius: 1.9
+PAngle: 65.0
+PAni: particleexp01
+Miss Factor: 1 1 1 1 1
+BeamSound: 146
+WarmupSound: 153
+Shots: 0
+ShrinkFactor: 0.1
+ShrinkPct: 1.8
+Range: 800
+Attenuation: 0.25
+Beam Piercing Effect: exp04
+Beam Piercing Radius: 8
+Beam Piercing Effect Velocity: 60
+Beam Piercing Splash Effect Velocity: 60
+Beam Piercing Effect Variance: 0.0
$Section: (shouldn't matter so I truncated)