I was an early backer and user of the now-defunct firearms SE a few years ago.
Perhaps this time around it would fit better into the larger Weapons proposal?
There have been at least three separate attempts at a Firearms Stack Exchange.
The first, some years ago, made it into beta before being killed. It might have survived under the new standards.
Two subsequent Area51 proposals (just barely) failed to make it out of Definition! (The first was renamed and given an expanded scope as "The Armory," and it was rebooted with the same scope after lingering for a year.)
Therefore, my money now is on the even broader Weapons proposal.
Firearms are great! But if they can't make it out of beta, it's a lot better to simply be a subset of a broader proposal. Weapons is like Stack Overflow to, well... weapons. Catapults, yes (thank you, Helmar). But also guns.
Once it's published, and gets bigger, we could consider splitting it. But until then, we can gain from the combined knowlage of people who might know mostly about guns, but a little about swords as well (I know a few). Or Tanks, for that matter. And a lot of F-16 pilots like guns, as well.
Combining makes everyone stronger, not weaker.