I think the 'reload while you melee' thing works for all the weapons... very handy anyway. If you get low on ammo, just make sure you hit R before you start hitting stuff with melee, otherwise you'll still have no bullets in the gun when you hit the melee limiting thing.
I used to love the Autoshotty for raw power (and the fact that I almost always ran out of ammo with the Assault Rifle) then I discovered the magic of burst fire - quick click on each enemy, taken from a crouching position and they all go down with about 3 bullets fired per head. The thing's really quite scarily accurate when you're holding still and crouched, at least for the first few shots, and using quick bursts of fire will have the accuracy returning to full in between shots.
It's not such a good one to just empty into the torso of a tank, although if you've got some distance then the spread on the shotgun probably makes the rifle the better choice even for that situation... so long as you can keep your distance.
Heh... I remember one time the tank came charging over, soaking up fire all the way, everyone around me bolted and I just held position firing like a nutter into the oncoming wall of meat (I knew I wouldn't be quick enough to outrun him anyway)... he got close, I'll give him that, but he was dead before he managed to punch me.
