I have noticed if im fighting a person and i shoot the gun out of their hand then i kill them before they get back to it i can pick that gun up then search their body for an additional gun of same type and condition. I look in my inventory and it shows up as one but i can hand one to a companion and i still have another in my inventory, if i shoot one of them once and i guess degrade it a hair past the other they will then show up as 2 in my inventory from then on. This does not happen EVERY time i do it but it does happen more often than not.
I didnt know if anybody else has had this one or not, it took me a bit to actually realize this since they only registered as one or two but id unload at my house and id have double or triple cause i put lets say a hunting rifle in then id have more in my inventory when id look

Have you repeated the initial cause? Or just assumed it after noticing the effect.

I keep finding this kind of thing with armor. But never had it with weapons.

Yeah, it happens often when im figting fiends near new vegas and it did it alot with missle launchers when i attacked the boomers. Id shoot them dang weapons out of there hand so they couldnt fire on me and id find 3 or 4 launchers with 2 or 3 guys in many places but most often with guns on fiends or vipers cause if i fight ncr or legion they are tougher opponents and they get the kill shots, not toying with like the easier enemies. I got back through the outer regions of vegas alot and it happens over and over. Not every single time but like 60 to 70 percent of the time i get two guns. I even have tried when i noticed it right away that 1 guy dropped 2, ill look in my inventory and see one then i can fire it and the other will appear with a cost right above the one i just fired or if it reads one ill hand one off to a companion or drop it and another will be there even after only one was noted in my inventory. If i place it back itll read one. I have to do something to make the game see it differently.

i cant repair it with the same one if it only reads one... if i got 2 rifles and i go to repair with the other and click Y i will notice there are 3 or 4 rifles sometimes there. AT first i always looked if off to just not noticing but now i have redone the glitch

That happens with quite a few items. It's like theres 2 stacks in the same slot. Pull the top item off and you find another stack underneath. Boones beret does it but a little differently. If you ever take his beret after his quest is all done and give it back to him, you end up losing the one that you scored for yourself.

I've had this happen constantly, and have gotten a number of 'free' full-CND items from it. If it's a light piece of clothing such as a Powder Gang Simple Outfit I sometimes end up with multiple 'extra' ones 'underneath' the partially repaired one displayed in the pip-boy screen. It also works the other way for me; I have had a fully-repaired item and then gotten a damaged one, and they stacked together in my inventory after a while even though initially they displayed separately.

I have also noticed this sometimes happening after a session of using spares to fix things up for sale; I will have, say, 2-4 fully-repaired copies and one damaged one, but the screen will only show the damaged one until I put it in a storage container, at which point the 2-4 fixed ones will show up. The odd part is, the full-CND ones would show up in the repair screen while I still had the damaged one in my inventory...