One of the things about fiction is that it gets almost everything wrong. It isn’t just guns. It’s professions like spies and snipers, cars, boats, planes, programming/hacking, radios, technology, etc. And those are just the areas that I personally know they get wrong, because I know more than the average person in those areas.
Some people judge fiction way too harshly for inconsequential but inaccurate details which only serve for narrative structure. There are actually tons of authors who get all of these details right, but you almost never read their books because if they can get them published at all, nobody reads them, because they absolutely suck. An author that gets these details right and is actually a good storyteller is extremely rare. It’s basically a list consisting of Tom Clancy and John Le Carre.
It’s just a pet peeve. At some point you have to let it go, or you’ll end up wasting your time writing blog posts begging authors (who largely don’t care) to talk to you so they won’t get inconsequential details wrong.
A modern author who's fairly good in this regard is Andy Weir; the main thing is you have to do a ton of research while writing and have trusted sources (I think Clancy had many) to rely on when mulling over the details.
The tough thing is, once you get "above average" in terms of accuracy, those of us who like to be a little more pedantic will grade on a curve!
When a certain now famous (in those circles) narrator was first getting started he mentioned on his FB page he wanted help with pronunciation of certain military terminology. I offered to help, knowing people in many fields plus my own. And ... my goodness, the absolute poor quality of some the writing he sent me. One author would use the full terminology for every firearm every time he looked at it, picked it up, loaded it, holstered it, drew it, released the safety, fired it, cleaned it, thought about while in the shower, whatever. You got tired of reading about the "Heckler & Koch HK45 Compact Tactical (HK45CT) MK-24 Mod-0" fully spelled out three times a page.
And then the author with his own specialty started writing about my field ... oh so badly.
So, knowledge of weapons doesn't translate in knowledge of writing (or vice versa). My only criteria any longer is just don't say "clip" unless your character has scored himself a Mauser C96 or similar and we're good.