Took a bug out and it's running lickety-split plus there's more ammo now - but don't go wasting it.
1) crates always reappear next time you visit a map in the place you last saw them.
2) Hold down SHIFT while aiming for precision shooting.
3) until you get tooled up you're better off taking a stealthy approach - only shoot the ants that become alerted
Also, maybe you should shut down all other programs, some maps can lagggggggggg.