The Fallout 1 Red Ryder LE BB gun can be devastating with the right character build. Super low action points to use, and the ammo weighs almost nothing. With a high luck sniper build character, it can fire up to 3 times per turn, inflicting multiple critical hits.
It’s only available by getting a particular special encounter, which makes it feel pretty special.
I proudly killed the Master with it.
The New Vegas ‘That Gun’ isn’t even the first Blade Runner gun in Fallout. The first two games had the .223 pistol, which was pretty good for the midgame. The ‘That Gun’ is a double reference both to Blade Runner and the old games.