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I choose the AC/5, (more ammo, less heat)
for strait up combat platforms, Autocannon. for vehicles who need the extra damage against non hardened targets such as engineering platforms I will take the rifle.
the Rifle is cheap and deals 8 damage to anything with a BAR Rating of 7 or lower. this gives it extra damage against buildings, support vehicles, and Battle Armor, making it viable for the "use the gun to destroy a bridge joist" or whatever else.