Rapid Fire Pistol.

This one allows the Snub Pistol to fire like the Gorgon Pistol. You need a level with a Gorgon Pistol and Boomshield on it.

First pick up a Gorgon Pistol, and find a shield. Stand over the shield, and quickly fire the gorgon pistol, and press Left on the D-Pad and X. You should pick up the shield, and now being holding a Snub Pistol. You have to do the above pretty fast to make sure it works right, and is difficult to get working.