https://imgur.com/mv4Pl3V
https://imgur.com/JjpCcjI
The first is from OA, and the second from NV. The only difference is a cap was added to the end of the butt of the rifle. That new cap somehow becomes transparent in 1st person in NV or TTW. I only noticed it because I was using Roy's FOV Slider to set my FOV to 90 degrees.
I'm not sure how to deal with this. At the moment, my readme for Real Gauss Guns tells people to stick with the default FOV or live with it. In TTW, I change the 1st person models for the NV gauss rifles to the OA gauss rifle model. So it's not a big issue in TTW, but I'm surprised that more NV people haven't noticed this quirk. Probably because the default gauss rifle in NV is basically worthless, being a pretend plasma rifle that only does explosive damage... and hence susceptible to that nasty explosive damage bug in NV that means that often, shots go right through the target, so you end up shooting at their feet and hoping for splash damage.
That was the ENTIRE REASON I made my Real Gauss Gun mod - it changes the gauss gun to a nice ballistic weapon that actually works. I love using the gauss rifle in NV and TTW with my mod. It's my go-to weapon of choice. But now that I love using it AND I'm using a wider FOV, now I have noticed the end of the NV gauss rifle is missing.
EDIT: Here's what the NV gauss rifle normally looks like in 1st person with a wider FOV:
https://imgur.com/a/1Eux3KM
EDIT 2: If you notice something funny about the wall in that screenshot, that's because the Metro - You Are Here mod was dirty... really REALLY dirty. I've since made a clean version for TTW. That snapshot I did to show how bumping walls in GECK can give you funny issues.