Vigilance is a 12.7mm Pistol owned and used normally by Blackjack after getting it from Stable 99 in the My Little Pony Fanfic, Fallout Equestria: Project Horizons. You can find it in doc Mitch's house in a safe to the left right when you walk in his bedroom on an angel from the floor and wall.

Fallout Equestria (c) Kkat
Project Horizons (c) Somber