So in the beta I'd come across someone who'd be using this, and he'd be insanely good with it. He'd be killing me behind cover, on roofs, etc etc. Yet when I gave it a go, I couldn't hit a thing with it. I'd get a few hitmarkers here or there, but that was it. Well, turns out I was using it wrong. It's not meant to be used as a grenade launcher, but as something different entirely.
Here's how it works:
The projectiles are little balls that explode, much like grenades. The difference is that these babies can explode mid-air. You don't have to pop them yourself, you simply lock on to something and let the gun do the rest. Now when you lock on to something, the ball will pop 3 metres behind that something. So say someone's hiding behind a wall, you lock on to the wall, and shoot just over it. The ball will go over the wall, and explode, in mid-air, right behind it, damaging the naughty rascal hiding behind it. I can't wait to give this a go later.
Here's a video explaining it:
There is some incorrect information in this video, because the ammo does in fact resupply from small ammo packs, just very, very slowly. I know this from personal experience.
So give this a go, it looks like great fun!