Model 3
Trejo Machine Pistol
I think it is the smallest full-auto weapon ever made. Even though not well known in the united states it was quite successfull in Mexico, with over 16.000 pieces manufactured by Armas Trejo S.A. Zacatlan between 1952 and 1972. Trejo litterally translates into Apple in english, hence the apple logo on the side of the slide. This little Tactical Machine-Pistol is a blowback action with unlocked firing from a closed bolt. Built for bursts rather than full-auto fire since the magazine capacity is quite limiting. When introduced to the Mexican market there was no prohibition against full-auto capabilities in small calibers like the .22 Long Rifle.

The NFA of 1934 made the import to US small since the 200$ tax of class-2 firearms was far more than the original value of the trejo. The Firearms Act of 68 finally slammed the door into the U.S. (therefore also to much of rest of the world) and finally the mexican government closed down domestic production of firearms for private purchase. The Trejo was also made in semiauto only, a longer BBL model with larger capacity (11-shot) called Modelo 2 came out and also a Modelo 3 in .32auto and 9mmShort/.380acp. (Could say more about them but they were not the Trivia).

Full-auto versions of the Modelo-1 is marked Tipo-Rafaga (selective fire type) and a little Lever with a "R" marked for Rafaga. In all practical senses it is identical to a M1911 which is known to many shooters.
The rate of fire is very high, ranging from 1300-1400 rounds per minute depending on what type of ammuntion you use (higher velocity = higher rate of fire). Bursts can be shot from about three rounds up to a blistring eight bursted out and unloading the whole magazine in 0,4 seconds flat. A minus for this type of construction would be the unreliable .22LR rimfire cartridge.
 

Trejo Modelo 1 Machine Pistol
Caliber: .22LR
Action: Unlocked blowback, closed bolt selective fire
Rate of fire: 1300-1400rpm
Magazine: 8-shot capacity single-row
Barrel: 3,15''
Sights: Fixed Ramp front open-notch rear