Has there ever been a bullet-weapon in the fallout universe that is more advanced than our real world? I know they were transitioning to energy weapons, but still. I can't think of any, but then I'm not a gun expert (when I played fallout 2 back in the day, I mistook the g-11 for a fictional future weapon unique to fallout.)
I'm not referring to fancy stuff like rail guns, tesla, electric, just good-old bullets. You know, like a fictional successor to, say, the real world's military m4/m16.

They do have Variations of AR-15's in Fallout New Vegas. There were also futuristic looking weapons like the G-11 you mentionned and P90's. But as far as really kitted out, tactical weapons go, i think they look out of place. A laser screwed onto a gun looks like it fits Fallout in my opinion, but holosights don't. Don't really know why though haha.

I *think* the 10mm pistol is a fictional weapon. At least I've never heard of it, but then back in the old days I'd never heard of the g11 either and that is a real-life weapon despite its fancy appearance.

The commonwealth appears to lack the west coast's gun runners faction, so it makes sense that they've instead had to make do with a lot of junky hand-made weapons instead of newly made pre-war gun designs.