It seems to me at least, these should be combined. Since flak already does half damage against most targets, I just added some extra heat.
Fluff: Developed at NAIS in 3030, these munitions are standard flak rounds with a strip of magnesium around the neck. Every fifth round in an burst has a red/green trail behind it about 150-meters after leaving the barrel. This is to avoid giving away the gunner's position.
Affiliation: House Davion
Cost Multiplier: 2
Used By: All Standard Autocannons
Game Rules:
Increase attack by 1 heat, 2 if rapid-firing.
Autocannons firing tracer flak ammo reduce their to-hit modifiers for night combat to +1 (rather than +2) and eliminate any dusk/dawn modifiers.
When used in attacks against moving VTOLs, aerospace units and WiGEs, tracer flak ammunition confers a -2 to-hit modifier.
Full damage against airborne VTOLs and aerospace units, or when fired against conventional infantry.
Half damage against all other targets (round down).