The Smokegun is a custom tool that is unique when compared to other weapons in teardown in that it can't do anything besides spawning a smoke particle generator. It is a demonstration of scripted particle effects introduced from 0.7.2. Instead of displaying the ammo, it says "Click to emit".
Settings[]
These can be accessed using "P".
Duration[]
1 second, 3 seconds, Endless
Amount[]
A little, Medium, and A lot
Color[]
Brown, Red, and Green
Gravity[]
None, Upwards, and Downwards
Drag[]
Low, Medium, and High