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.