In 1968, MGC developed MG-Blowback cartridge for open detonator type blow back operation for their blowback models. The cartridge is extremely simple in construction and does not look like a real cartridge at all. It is typically just a single-piece brass open "tube" closed at one end with a machined extractor groove, thus also known as open cartridge. The cap is plugged deep into bottom of the cartridge and fired by a thick detonator pin. The exploded pressure between detonator pin and bottom of cartridge produces the blowback effect. However, it is difficult to achieve stable blowback performance as it uses paper caps which left residue built up on the detonator pin and inside the cartridge. The cartridge is also very hard to clean after fired.