Grenades, Grenade Launchers, and proficiency

[Darrell Impey UK]

If I have a character who has proficiency in heavy weapons but not in grenades, and they fire a grenade launcher, do they receive a non-proficient penalty to attack or not?

[Xenocrat]

Yes.

[Kamyr]

No.

They are making an attack with a heavy weapon that uses grenades like rounds.

Weapon specialization won't apply since the damage is per the grenade, but they only need heavy proficiency.

[Xenocrat]

Oh I misread. Agree with Kamyr.