Reading up on forums at work, because work is dead (received 1 phonecall and 1 mail so far) and found this regarding the underslung GL bug:
According to technical support, the Developers have intentionally limited the grenade launcher attachment to one "resupply" from an ammo pack, after which it is supposed to stop reloading ammo. The "stop reloading ammo" part is bugged, and often either doesn't stop reloads or stops it TOO well and prevents the weapon it is attached to from reloading as well. They don't want grenade spam from grenade launchers...
So, it's intended that you can only reload your UGL from an ammopack
once before having to resupply at an equipment terminal.
Think I'm going for the VX6 (vs. the Solstice SF) for my engi anyway. Maybe make a long range build with the battlerifle for specific situations. And will still have to mull over whether to make a Nova (shotgun) build or not. I'd need a 4th build slot for it (1) short range ammo - support; 2) long range ammo - support; 3) base defence - turret repper/gunner & AP mine; 4) CQC gung ho shotgun sprayer)