Defense Review, long known for its accurate reporting on the gun front, had another head scratcher:
The GSh-18 also apparently utilizes double-column magazine that transitions to single-column feed at the top for more reliable feeding, just like the P7 M13 mag.No, no, no, no.
A double column magazine that narrows to a single column at the top is less reliable than one that feeds left-right-left-right because the spring is having to squeeze two stacks of cartridges through one hole. The spring has to be stronger and the magazine is more sensitive to dirt and debris. The advantage you gain is that you can use a single feed ramp and don't need to make your pistol's slide as wide as, say, an Uzi to accommodate the double feed ramps. This is why weapons where narrowness is not important, like rifles and machine pistols, do not have magazines that narrow to a single column on top.
Remember: Pat Rogers calls it the "Errornet" for a reason.