Just skip blast gun, and use ump and shotgun till you can get carbine. It will save you from suffering later.
Now, if you don't know what I'm talking about or how to use full-auto guns as a sniper, that's ok big Z will tell you the tricks.
- go to options/setting
- Enable iron sights: False
- Crosshair dot: True
- Crosshair scale: 1
next
- go to Controls
- Switch weapon: E or Q
- Melee weapon: E or Q (depending on what you picked first)
- Spawn menu: 1 or 2
- Third-person: 1 or 2 (depending on what you picked first)*you could keep it as H, but 1/2 is probably better*
If you have done that, then you are all set for the needed options.
that tip will also help you