I've upgraded a a lot of my weapons but i cannot use secondary fire on any of them.

I've played through a fair number of levels but as it goes on it becoems more of a problem.

I've checked key bindings and secondary fire should be RMB, have altered, then changed back again but not worked.

my RMB is definitely working as it recognises it when i change it back to RMB from another key

i changed it to MMB and that didn't work either, so it feels like a bug

anyone had the same problem and know a fix?