[SG] Hand-held grenade launcher ?

Hello everybody

I just finished painting up a bunch of mercenary figures. and I'm
stumped on
how to class one of them for Stargrunt. It's

SGM 18D Female Mercenary trooper with grenade launcher

Her weapon is a small grenade launcher similar to those you might see
slung
under a rifle, but as a stand-alone weapon with a shoulder-stock.
What would Firepower and Impact die be for that ?
Assaukt rifles with grenade launchers increase in FP by 1 for an
attached
GL, so I would be inclined to give it an FP of 1.
But what about the Impact die ? D8*  like an auto-grenade launcher?

Greetings
Karl Heinz