Try with these values:
explosive charge spawned
MinEF=1000
MaxEF=1000
AP=0
MinRadius=0
MaxRadius=0.1
Rocket new zone
Multiplier=1
Flotability=0
HitPoints=500
Destructible=Yes
Armor Level=0
Critic Flotation=0
Critical=No
FloodingTime=1
CargoType=None
Crash Depth=1000
If the Avenger still explodes, try reducing charge's Min/MaxEF and rocket's HitPoints to 2 and 1 respectively (I am not sure whether decimal numbers are valid HP entires; if they are, something like 0.25 and 0.0625 respectively, would be even better...)
If the Avenger finally doesn't explode but the dummy rockets don't disappear, try increasing a bit the max radius of the explosive charge and moving gun's muzzles away from the dummy rocket. It is possible that if an explosion happens within an object, that object can't get damaged (i.e. the explosion must impact its damage box from outside)