I put the 1/2b -1 because the gun's big brother (Which is effectively an assault cannon) deals less damage than other assault cannons (minimal difference, but there) and has 1/2 -4 penetration, which is about the same as having a normal assault cannon's penetration and halving the armour.
Good catch on the smart armour.
If a guard saw you running around with a 30F weapon (IE cutting edge milspec) hell yes is he going to prioritize you as a target! much like if you were wielding a laser, or any other cutting edge weapon.
as to why make it an assault rifle rather than an exotic weapon or the like: Exotic weapons that give 1/2B penetration already exist, they're called lasers. This is for all intents and purposes an assault rifle...
Hang on, if we cut the underbarrel slot from it then it can't take a Gyromount. without access to a Gyromount or gas vents, it'll be very hard for an enterprising young player to mod it for full auto and let rip. Let's double the penalties for recoil while we're about it, as a mini-gauss rifle is going to have serious kick.
Does that seem a better balance?