"Six men came to kill me one time. And the best of 'em carried this. It's a Callahan full-bore auto-lock. Customized trigger, double cartridge thorough gauge. It is my very favorite gun … This is the best gun made by man. It has extreme sentimental value … I call her Vera."
The Callahan Full-bore Auto-lock was a weapon with armor-piercing capabilities. Jayne Cobb owned one of these weapons and named it "Vera".
Although not obvious, its name seemed to indicate that the weapon can dynamically switch bore sizes depending on the cartridge's size that the user desires. The weapon could not be fired in space, as it required oxygen to ignite the projectile.
The "Callahan Full-bore Auto-lock" prop also appeared in the movie Showtime (2002) with Eddie Murphy and Robert De Niro, and is modeled with (mostly) bolt-on parts on top of a Russian Saiga-12 Kalashnikov-pattern semi-automatic shotgun. In the Russian language, the word "Vera" (вера - рус.) translates as: faith, trust, belief, and means serious hope. Also, it is a woman's name Vera (Вера - рус.).
On Halo 3 and Halo 3: ODST, Adam Baldwin's characters often use quotes like "Say hello to Vera" during battles whenever he throws a frag grenade.
The gun's apparent manufacturer is likely a reference to the "Dirty Harry" series, named after Clint Eastwood's character Harry "Dirty Harry" Callahan.