Just picked up the Gast's Rifle today. Until I got my First Win that unlocked the +4 ammo per clip upgrade, it was pretty useless for me. The trouble is that I've yet to master the projectile speed of the SLD's rifles. I'm getting better, though, so the Gast's is looking like it will probably be my standard loadout. I've been using the Proxy 'nades, too, which are pretty handy.