Here’s another Weird Science Gadget for Pulp Cthulhu (p.86ff, Pulp Cthulhu rulebook). Scroll down for a PDF to download and print.
The Sleeve Gun is a concealed, spring-loaded weapon which extends a small firearm from a specially designed bracer worn around the wrist. This device can be used to quick draw a firearm.
During combat, an attacker with a Sleeve Gun may draw their hidden firearm and attack without needing to have their weapon “readied” to gain +50 DEX when determining position in the DEX order for combat (as per the Quick Draw Talent, p.25 Pulp Cthulhu rulebook). A Sleeve Gun is typically used with a .22 Short Automatic or .22 Derringer (causing 1D6 damage, p.402 Keeper Rulebook or p.251 Investigator Rulebook).
To build: parts cost $250, requires 1d10+5 days, and a successful combined Hard Mechanical Repair and Hard Art/Craft (Weaponsmith) roll.
Image from The Wild Wild West (1965-1969 CBS).