The Glock pistol design allows easy modification into “select fire” or “full auto only” modes. This modification can be achieved using a variety of “low tech” methods, but all rely on the disengagement of the trigger bar from the striker tail at the appropriate moment in the firing cycle.
– Steven Pavlovich, “Select Fire Device Found on Glock Firearms Seized by Western Australia Police” (2014)
Machine pistols – that is, selective-fire or full-automatic pistols, not submachine guns – have few real applications. Entry teams use them sometimes because they are more manoeuvrable or can be used one-handed, for example while holding an entry shield or forcing open a door. Bodyguards occasionally use them because they are easily concealed even wearing a business suit yet offer substantial firepower allowing them to disengage from an attack on their patron.
It is important to realise that machine pistol are real close-quarters weapons. Typical range is supposed to be 3 to 5 metres according to firearms instructor Timothy Mullin. For shots at longer distances, they are to be used on semiautomatic to ensure hits.
The pistol manufacturer Glock has offered a machine pistol variant based on its successful Glock 17 semiautomatic pistol since May 1987. However, the Glock 18 machine pistol (GURPS High-Tech, p. 101; Investigator Weapons 2: Modern Day, p. 63) is extremely rare, as it is only sold to government agencies, and even those have few applications for such a weapon, as outlined above.
Already in 1987 Jorge Leon of Venezuela invented a selector which could be added to any normal Glock to convert it into a selective-fire machine pistol. This received US Patent #5,705,763 (6 January 1998). Basically, the backplate on the slide of a Glock can be removed and replaced with a new aluminium backplate with a cross bolt that extends about 14 mm to the rear and adds a mere 17 g to the weight. The replacement requires no special tools or skills and takes about one minute. When the cross bolt is pushed to the left an arm is extended inside the slide which depresses the weapon’s disconnector and thus allows full-automatic fire at some 1,200 shots per minute. Since 1998, this invention is offered commercially as the FSSG fire selector switch (Investigator Weapons 2, p. 65). It will fit any Glock pistol except for the slimline Glock 42, Glock 43, and Glock 48. This too is only sold to government agencies and dealers. The FSSG costs $275.
Source: ATF
A similar conversion has been available commercially since 1993 from Lakeside Firearms in Maryland.
Since the year 2000, a number of companies have copied the device, mostly directly, sometimes merely in spirit. Many are even marked “Glock,” although the parent company has nothing to do with them. Copies have appeared made in Argentina, China, the Philippines, and Venezuela. Many have been sold on internet platforms all over the world; in 2017 they even appeared on large sites like Amazon and eBay. These are extremely cheap, prices ranging from $12 to $70 plus shipping. Sometimes these have been offered as parts for airsoft guns. Once the platform providers realise what the items are, they are usually taken down, but there are always people who manage to buy them anyway. In some places the selectors were legal to buy, but illegal to install, in others like the USA the part itself is deemed a “machine gun” and thus subject to relevant laws. In recent years, the sellers shipping them internationally have tried to conceal their nature by using falsified customs declarations, marking them as automobile parts, screws, etc. Thousands of the devices have been sold in the USA alone. On the black market, the imported selectors sell for about $500. Glocks converted with such devices have appeared worldwide from Australia to Germany to Venezuela, ranging from full-size Glock 17s to compact Glock 23s to sub-compact Glock 26s – the usefulness of a full-automatic pocket pistol with a 10-round magazine at typically over 1,200 shots per minute is questionable, but hey.
However, the device is so simple that any machinist can copy it, and indeed many craft-produced copies have appeared. It has been shown that the device can be even be made with a hacksaw and a file. Further, the selectors have even been built using 3D printers. CAD renderings appeared as early as 2013. Installation of the home-made parts requires removal of a bit of plastic from the trigger housing and cutting a notch into the rear of the pistol grip frame, which can be done with an exacto knife, as well as some filing of the trigger bar cruciform.
In Games
In GURPS, change RoF to 20 and Malf. to 17. Installation requires an Easy Armoury (Small Arms) or IQ-based Guns (Pistol) roll. Constructing the device requires an Easy Armoury (Small Arms), Machinist, or Mechanic roll.
In Call of Cthulhu, change ROF to 1(3) or 40 and Mal to 97. Installation requires an Art & Craft (Gunsmith), Firearms (Handgun) or Mechanical Repair roll. Constructing the device requires an Art & Craft (Gunsmith) or Mechanical Repair roll.
In Delta Green: The Role-Playing Game, treat the converted weapon as a Medium Pistol with Lethality 10% (Delta Green: Agent’s Handbook, p. 97). Installation requires a Craft (Gunsmith), Craft (Mechanic), or Firearms roll. Constructing the device requires Craft (Gunsmith) or Craft (Mechanic).
At the Movies
The menace of a converted Glock 17 is demonstrated by the Joker in The Dark Knight (2008), by a Stockholmed Ella Pierce in Numb3rs #4.8 (2008); by a bad guy in Son of a Gun (2014), by the Polish Accountant in Twin Peaks #3.16 (2017), and by a bad guy in SWAT #1.1 (2018).
Shooting Dice 
