Green’s Dictionary of Slang

shooter n.1

1. [mid-19C+] (UK/US Und.) a gun, a revolver.

2. [20C+] (gambling) the player currently throwing the dice in a game of craps.

3. [1940s+] one who fires a weapon, an assassin.

4. a press photographer.

In derivatives

shootered up (adj.)

[1950s] armed.