You could try adding an explosion code block to the weapon_equip listing, the one below has an explosion code block so it produces a large explosion effect on impact (style over content I suppose :))
You could increase the explosion damage levels and radius to suitable levels.
[Explosion]
nickname = GAU35_explosion
effect = ku_mine01_blast25
lifetime = 0.000000, 0.000000
process = disappear
strength = 10
radius = 1
hull_damage = 20
energy_damage = 0
impulse = 0
[Munition]
nickname = GAU35_ammo
hp_type = hp_gun
explosion_arch = GAU35_explosion
requires_ammo = false
hit_pts = 2
hull_damage = 300
energy_damage = 50
weapon_type = W_Pulse01
one_shot_sound = fire_laser1
munition_hit_effect = ci_pulse_04_impact
const_effect = ci_pulse_02_proj
lifetime = 1.200000
force_gun_ori = false
mass = 1
volume = 0.000100
[Gun]
nickname = GAU35
ids_name = 463203
ids_info = 463202
DA_archetype = equipment\models\weapons\br_mass_driver.cmp
material_library = equipment\models\br_equip.mat
HP_child = HPConnect
hit_pts = 6000
explosion_resistance = 1.000000
debris_type = debris_normal
parent_impulse = 20
child_impulse = 80
volume = 0.000000
mass = 10
hp_gun_type = hp_gun_special_1
damage_per_fire = 0
power_usage = 85
refire_delay = 0.140000
muzzle_velocity = 650
use_animation = Sc_fire
toughness = 1.000000
flash_particle_name = ci_laser_04_flash
flash_radius = 10
light_anim = l_gun01_flash
projectile_archetype = GAU35_ammo
separation_explosion = sever_debris
auto_turret = false
turn_rate = 90
lootable = true
LODranges = 0, 20, 60, 100
Another possibility is a missile-gun, essentially when the missile motor burns out the munition explodes, this is intended to produce a flak barrage
[Motor]
nickname = li_battleship_flak_turret01_motor
lifetime = 1
accel = 166.666702
delay = 0
[Explosion]
nickname = li_battleship_flak_turret01_explosion
effect = li_flakcannon01_impact
lifetime = 0.000000, 0.000000
process = disappear
strength = 100
radius = 16
hull_damage = 10.000000
energy_damage = 0
impulse = 0
[Munition]
nickname = li_battleship_flak_turret01_ammo
explosion_arch = li_battleship_flak_turret01_explosion
hp_type = hp_gun
requires_ammo = false
hit_pts = 2
one_shot_sound = fire_capship
detonation_dist = 4
lifetime = 5
Motor = li_battleship_flak_turret01_motor
force_gun_ori = false
const_effect = li_flakcannon01_proj
HP_trail_parent = HPExhaust
seeker = DUMB
DA_archetype = equipment\models\weapons\li_rad_missile.3db
material_library = equipment\models\li_equip.mat
mass = 1
volume = 0.000100
[Gun]
nickname = li_battleship_flak_turret01
ids_name = 263383
ids_info = 264383
DA_archetype = equipment\models\turret\li_turret04b.cmp
material_library = equipment\models\li_turret.mat
HP_child = HPConnect
hit_pts = 4800
explosion_resistance = 1.000000
debris_type = debris_turret_small
parent_impulse = 20
child_impulse = 80
volume = 50.000000
mass = 10
hp_gun_type = hp_turret_special_6
damage_per_fire = 0
power_usage = 0
refire_delay = 0.142857
muzzle_velocity = 83.300003
toughness = 1.600000
flash_particle_name = li_flakcannon01_flash
flash_radius = 15
light_anim = l_gun01_flash
projectile_archetype = li_battleship_flak_turret01_ammo
separation_explosion = sever_debris
auto_turret = true
turn_rate = 90
lootable = false
dispersion_angle = 5
[LOD]
obj = Root
LODranges = 0, 450
[LOD]
obj = barrel
LODranges = 0, 500