Not really:

* There is always someone with a bigger gun

* There is always someone who wants to steal your gun/ammo

* There is always a bigger gang that wants to steal your gun

If your solution is to join up with others to make your gang the biggest/best armed and enforcing a monopoly on the use of violence, congratulations, you've either reinvented Warlordism, or in the best case, reinvented the idea of a police force, depending on whether or not the head of the gang answers to a civil authority whose legitimacy comes from something other than "might makes right".

All that said, I don't mean that firearms aren't at all useful, just that they aren't more useful than other important tools. You for a group to be able to defend itself you will find that basics like picks, shovels, sledgehammers, crowbars, hammer and nails, axes and hatchets, saws, ladders, wheelbarrows etc. are all at least as useful as a firearm.

Generally speaking, making the other guy waste his ammo can be a winning strategy.