[LyndsySimon]

Probably the most effective of these if you have 12ga ammo available is a “bang stick”. It’s basically a 12ga shell in a tube, with a spring that will force it into a firing pin when it’s pressed against something and trips a small lever holding back the spring. They’re used in shark hunting and for self-defense by divers against sharks.

Here’s a commercial one, which has a safety pin that must be removed before it will fire: http://www.billsbangsticks.com/12-Gauge-Powerhead_p_17.html

In an insurgency situation, devices like this are best used to obtain something better. Only being usable for a single shot isn’t necessarily a huge disadvantage, especially if there are multiple people using them at the same time. Pressed against heavy clothing, they also make surprising little noise. The “Liberator” .45 pistol was made by the US with the intention of airdropping the, to the French Resistance in WW2. In reality, almost all of them ended up at the bottom of the Atlantic. The Sten 9mm SMG didn’t cost much more to make and was much more effective.

[jpitz]

I remember one employed by the protagonist in one of Clancey's books, Without Remorse.