I found it strange that the base-game Gauss Rifle is considered an energy weapon, consuming Micro Fusion Cells and no physical ammunition even though it clearly fires a solid projectile. This weapon is my answer - a Guns-skill electromagnetic coilgun that consumes physical bolts, and it's assumed that there is a battery in the stock to power it.

Parts Used

I started with the Bozar mesh from the Gun Runners' Arsenal DLC and removed the barrel. I then added the scope and barrel from the YCS/186 unique Gauss Rifle.

Apocrypha

Lore-wise, I imagine this gun was a rejected entry in a U.S. Army procurement trial looking to replace the M72 Gauss rifle that we see in Fallout 2. In my head-canon, the German-made M72 was excellent but expensive, and the Army was looking to replace it with something cheaper and domestically-produced to outfit its troops during the build-up to the liberation of Anchorage. Ultimately, they ended up adopting the Gauss Rifle that we see in the Operation: Anchorage DLC and Fallout: New Vegas, whereas this rejected bid sample never entered mass-production.