I use a weapon mod that technically was suppose to have two modes to it; Assault Rifle and Grenade launcher. The specific weapon is the M41A Pulse Rifle from the aliens movies. It came with a grenade launcher that plain and simple does not work. The 95 .5mm shots per clip is great for keeping enemies pinned down. I've tried switching over to the grenade launcher with grenades in my inventory but it never works.

Have any of you encountered weapons with multiple functions that actually worked?

Just for the record this weapon is one of my favorites; high ammo capacity, very common ammo, high weapon health. The max damage on the weapon is 56 with 100 on small guns however for some reason on PL its damage has nearly doubled (dmg 111) while on PL. Reverts back to dmg 56 on the mainland.

You probaly need FOSE. Do you need to use the keyboard to switch modes?

No, it is set as a secondary weapon in your inventory. Just click on it as if you were equipping any weapon. Thanks for the quick reply.