Well, be aware that lemmy in general is pretty leftist, and liberal in the American sense isn't the same as when used in the context of global politics.
You specified the second amendment, so there isn't likely to be too much hassle over that, but it's something to be aware of when the socialists and anarchists scroll by.
Also, there are similar communities out there, so you might want to check those out and join in the conversations about the U.S. situation as it comes up.
There are conservatives on lemmy, and most of them do remain civil when interacting with people that aren't, though it isn't by any means a guarantee.
!armedqweers@lemmy.blahaj.zone aka the armed gay agenda and !armeddemocrats@midwest.social tend to be compatible with what you're proposing.
There's communities like !armedworkers@lemmy.ml as well that cover some of the same ground, but probably wouldn't align well with your overall outlook. Tends to run a little further left.
Iirc, !guns@lemmy.world is fairly friendly to everyone, so I would think you'd at least enjoy checking it out.
If you substitute sh.itjuts.works, lemm.ee, and midwest.social for lemmy.world in the above link, they have gun focused communities too, with naming varying degrees of activity.
!resist@fedia.io is a solid hub for general resistance to oligarchy and fascism.
There's others out there, I know, but those are the ones I've find t to be most likely to be friendly to a US liberal that's also a firearms advocate of some stripe.
Myself, I'm further left than that, and a bit more radical in my views regarding what resistance should end up being, but that's tangential and only brought up as a means of letting you know that even folks not fully aligned with your political views can still be open and friendly.