Seconded, largely.
There are a lot of projects out there aimed at making FDM prints stronger - from better materials to inert/vacuum atmospheres, fiber injection, and various annealing processes….
But there are a lot of things you just wouldn't want to do with a 3d printer - or would do only as a novelty. Dimensional tolerances with FDM get kind of hard to maintain. In my own destructive testing of my 3d printed parts, they tend to be vulnerable to shattering under sudden shock. I can stand on a part or put a few hundred pounds on it more - and it will survive. But a good little smack with a hammer and pieces go flying.
So my experience is to not use them in things like a gun.
There again, we are getting much closer to desktop metal sintering or metal based FDM processes which could give us much better parts. Still - the barrel would likely need to be machined and given some variety of lining to be able to compare it. Although, most barrels aren't serialized, so if you work from a barrel back to an upper receiver and bolt/carrier - a 3d printed gun becomes more practical, but only just.
Not much reason to 3d print a firearm, and even then - a practical FDM print would probably look much different from existing firearms because the materials have such different properties from steel.