Your heavy blaster rifle just ran out of ammo and there's an angry Trandoshan engaged with you who's trying to claw your face off. Can you rifle-butt him in the head as an attack?
I think the improvised weapons rule does a nice job of covering this. I can see treating the butt of a pistol grip as a small improvised weapon. I'd probably do the same for a rifle butt, though if it was a really big weapon like a rocket launcher, maybe that could go up to a medium improvised weapon.
Does that sound reasonable? What do you guys think?