A fully automatic submachine gun
that is chambered for the venerable .45 ACP
cartridge. The MAC 10 is a very fast and effective tool for converting good money into noise.
Economically manufactured using stamped parts, this gun is a good example of working simplicity and functionality in design. Operating on the blow back principle and firing from an open bolt, achieving a high rate of fire is possible. Firing from an open bolt means that there is no mechanical locking of the breech and the bolt is only kept in place by inertia and the tension of the recoil spring. This makes it cycle very quickly and prevents cooking off, the spontaneous discharge of a cartridge due to very high temperatures.
The MAC 10 borrows design philosphies from the most excellent submachine gun, the UZI.
The supposed cult following among special force operatives probably refers to a genuine cult following among spec ops wannabes who learn (and node what they "learn") about firearms from first person shooter games like Half Life and Counter Strike.
It never was designed to replace the m1911 as the standard sidearm of the US Armed Forces as suggested by Jhrulith. The 1911 was replaced by the M9 Beretta 92 in 1989.