Completely banning guns in a roleplay in my opinion is a rather poor decision, it limits the possibilities of the decisions made by characters and the the writers themselves. I think the toss-up between conserving ammunition and conserving life forms a fundamental part of any post-apocalyptic as it's the strongest case of balancing scarce resources in order to try and get the best result. Unfortunately it does have a big potential to be abused and become overpowered, something which should be very carefully monitored by the GM and the players themselves. Whilst it's relatively easy to blame it on the GM, I think there's a strong case for player responsibility existing too. I think natural limitations are the best way to implement, the longer the roleplay goes on, the more scarce the bullets and guns get; especially with wear and tear.

It mainly revolves around the fundamental of choice, especially when it comes to that almost cliche notion of one bullet left in the clip, do you use that on yourself or the mindless creature about to devour you?