Try this on for size:
$Name: Jackhammer IIEC
+Title: XSTR( "Jackhammer Enhanced Capability", -1 )
+Description: XSTR("
Bomb
Velocity 100, Range 2000, ROF 20.0
DPS 200 Armor, 20 Shield, 170 Subsystem
BAS 20.0
", -1 )
$end_multi_text
+Tech Title: XSTR( "Jackhammer Enhanced Capability", -1 )
+Tech Anim: none
+Tech Description: XSTR( "Jackhammer Enhanced Capability", -1 )
$end_multi_text
$Tech Model: JackhammerMK2EXT.pof
$Model File: JackhammerMK2.pof
$POF target LOD: 0
$External Model File: JackhammerMK2EXT.pof
$Mass: 35.0
$Velocity: 100.0
$Fire Wait: 20.0
$Damage: 8000
$Damage Type: HugeWeapon
$Arm radius: 250
$Detonation Range: 250
$Shockwave Damage Type: Shockwave
$Blast Force: 0.0
$Inner Radius: 0.0
$Outer Radius: 0.0
$Shockwave Speed: 0
$Shockwave name: shockwave01
$Dinky shockwave:
+Blast Force: 0
+Inner Radius: 7
+Outer Radius: 24
+Shockwave Speed: 0.0
$Armor Factor: 1.0
$Shield Factor: 0.1
$Subsystem Factor: 0.85
$Lifetime: 20.0
$Energy Consumed: 0.0
$Cargo Size: 20.0
$Homing: YES
+Type: ASPECT
+Turn Time: 0.5
+Min Lock Time: 7.0
+Lock Pixels/Sec: 25
+Catch-up Pixels/Sec: 0
+Catch-up Penalty: 15
$LaunchSnd: 96
$ImpactSnd: 101
$FlyBySnd: -1
$Rearm Rate: 0.02
+Weapon Range: 2000
$Flags: ( "bomb" "Huge" "No Dumbfire" "player allowed" "particle spew" "Spawn Jackhammer IIEC, 1" "Spawn MIRVDecoy, 3" "no lifeleft penalty")
$Trail:
+Start Width: 0.4
+End Width: 0
+Start Alpha: 1.0
+End Alpha: 0.0
+Max Life: 4.0
+Bitmap: missiletrail02
$Impact Explosion: ExpMissileHit1
$Impact Explosion Radius: 22.52
$Dinky impact explosion: ExpMissileHit1
$Dinky impact explosion radius: 22.52
$Piercing Impact Explosion: exp04
$Piercing Impact Radius: 11.26
$Piercing Impact Velocity: 25
$Piercing Impact Splash Velocity: -25
$Piercing Impact Variance: 20000
$Piercing Impact Particles: 10
$Spawn angle: 0
$Spawn angle: 30
$Pspew:
+Count: 1
+Time: 1
+Vel: 0.0
+Radius: 0.2
+Life: 0.1
+Scale: 0.0
+Bitmap: missilespew02
$Thruster Flame Effect: missilethruster02
$Thruster Glow Effect: missileglow02
You'll have to add a MIRVDecoy entry or remove that spawn entry.