I’ll give my personal opinion here because I do not have doctrine to back it up.
Short answer is yes. Catholics can own firearms for whatever reason they see fit. Defence, collection, hunting, etc. The key here is still “do no harm”.
Having said that (and seeing as I have no need or want to collect them), unless I live in an area similar to the wild, wild, west, where my family is in constant danger, I do not see the need to put myself in a position to harm somebody worst than I would have if I hadn’t owned one.
Thank the Lord, I live in a country where guns are not the norm, and the general population do not own one. The law is generally followed, and although there are some dodos who go out shooting or bombing people every now and then, it is fairly safe.
I did grow up in a fairly dangerous situation though, where mom had to sleep with a .38 under her pillow (no kidding), although again, thank the Lord nothing happened, but I do know of someone who “accidentally” shot someone because of road rage, just because he had a gun in his car for his “protection”. (The guy he shot died, yes, tragic.)
So, unless the situation is dire, I would rather not have firearms…just because it opens up the possibility of me harming someone “accidentally”.