Having nothing to do, I tried to table a ballistic weapon. I made a powerful cannon with a range of 2500 meters, used to destroy turrets and subsystems of capital ships from distance. Since it could destroy a fighter with a single shot (and I didn't want it to be used on fighters, only against major ships), the shield damage factor is very low and the bolt is slow moving. Only bombers can carry this weapon, and they can carry only a limited amount of ammo (30 shots for the Ursa, 10 for the Artemis, for example).
Copy this in a xxx-wep.tbm to insert the cannon in the game:
#Primary Weapons
$Name: GAU-73 Annihilator
+Title: XSTR("GTW GAU-73 Annihilator", -1)
+Description: XSTR(
"Ballistic cannon
Level 5 Hull Damage
Level 1 Shield Damage", -1)
$end_multi_text
+Tech Title: XSTR("GAU-73 Annihilator", -1)
+Tech Anim: Tech_Subach_HL-7
+Tech Description: XSTR("The GAU-73 Annihilator is a projectile weapon, firing a 50mm depleted uranium shell encircled by a plasma bolt. This cannon has a very limited ammo and is usually used to destroy subsystem at very long range. It is almost useless against shields.", -1)
$end_multi_text
$Model File: none
@Laser Bitmap: newglo3
@Laser Glow: 2_laserglow03
@Laser Color: 120, 120, 30
@Laser Color2: 120, 120, 30
@Laser Length: 10.0
@Laser Head Radius: 1.0
@Laser Tail Radius: 1.0
$Mass: 0.2
$Velocity: 350.0
$Fire Wait: 20.0
$Damage: 130
$Armor Factor: 3.0
$Shield Factor: 0.01
$Subsystem Factor: 2.8
$Lifetime: 7.0
$Energy Consumed: 0.0
$Cargo Size: 0.0
$Homing: NO
$LaunchSnd: 76
$ImpactSnd: 85
$Flags: ("in tech database" "player allowed" "stream" "ballistic" "shudder")
$Icon: iconPromS
$Anim: PromS
$Impact Explosion: none
#End
And add this in a xxx-shp.tbm to use the cannon with default FS2 Terran bombers:
#Ship Classes
$Name: GTB Zeus
+nocreate
$Allowed PBanks: ( "GAU-73 Annihilator" )
$PBank Capacity: ( 15 )
$Flags: ( "ballistic primaries" )
$Name: GTB Artemis
+nocreate
$Allowed PBanks: ( "GAU-73 Annihilator" )
$PBank Capacity: ( 10 )
$Flags: ( "ballistic primaries" )
$Name: GTB Artemis D.H.
+nocreate
$Allowed PBanks: ( "GAU-73 Annihilator" )
$PBank Capacity: ( 10 )
$Flags: ( "ballistic primaries" )
$Name: GTB Medusa
+nocreate
$Allowed PBanks: ( "GAU-73 Annihilator" )
$PBank Capacity: ( 20 )
$Flags: ( "ballistic primaries" )
$Name: GTB Ursa
+nocreate
$Allowed PBanks: ( "GAU-73 Annihilator" )
$PBank Capacity: ( 30 )
$Flags: ( "ballistic primaries" )
$Name: GTB Boanerges
+nocreate
$Allowed PBanks: ( "GAU-73 Annihilator" )
$PBank Capacity: ( 25 )
$Flags: ( "ballistic primaries" )
#End
Could be useful or I wasted my time only to create a piece of crap?
EDIT: added the "ballistic primaries" flag...

EDIT2: added the "+nocreate" line