All of the magazines are “double stack” double feed is different. A Glock (or most any other pistol that stagers the rounds in two columns) uses a double stack single feed magazine. An AR-15 on the other hand uses a double stack double feed magazine. You can tell the difference when you load them push straight down or push down and slide in and in the case of the M10-9 when you go to buy more of them.
The two on the left are double feed one with an even number of rounds the other odd. The one on the right is single feed.
