To answer the question about the sniper rifle. Yes you can use it provided it follows all rules set by the game host. Essentially what you'll be running around with though is a glorified springer shooting 330 FPS (assuming stock) or some possibly shooting hotter than that. You'd usually have to throw in a spring upgrade to get it to levels where it's going to run hot (or by buying a cheap clone which will break in a month of play because the durability of the parts goes down the stronger springs you get).
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE