Gas tank's don't actully blow up when you shoot them. Maybe if you hit the fuel rail or dmaage the engine in a way that sets fuel lines, maybe then. But nah, not realistic.
This game defenetley needs a .22 rifle. It's not all about PVP some people actualy want a rifle for hunting and some self protection. Also you could have .22 automatics. Crappy damage high rate of fire, lots of ammo.