The magazine catch of the Kalashnikov rifle is adjusted during installation in order to protrude more than 0,5mm but less than 1,5mm from the edge of the magazine well. There is a specific tool for this inspection but a simple gauge can be easily fabricated. The adjustment is made by carefully filing the area shown on the drawing until the dimensional constraints are achieved. Please refer to the file contained in the link below for the values and points of measurement.
Magazine Catch Inspection & Fitting