How about make the chaingun have a warmup time, like you press fire, and 5 secs later, the bullets come out. Maby time for the barrel to spin, start with a slow whop, whop, whop, whop, whop, whop,whopwhop, bdddddag.
I'd be in favor of that as an alternate fire mode for the chaingun that people might have bound to MOUSE2. So you could choose regular chaingun firing, or warmup & faster firing... that requires cooling after 100 shots or so.
Otherwise chaingun if fine as is. I admit I like it as a human to shred Tyrants and Goons. As an alien I've learned to dance around until they're out of ammo and finish them as they flee back for more ammo. It isn't too difficult in my opinion to empty a lone chaingunner since they usually lay on the trigger even when rounding corners.
Alternatively, *
gasp*, use
teamwork to take down a chaingunner. Share the damage, block his escape, chomp chomp chomp.