.40 Cal Px4 Storm Magazine. 17 round capacity - pinned to 10.
Calibre:.40 S&W
Finish: Black
Also compatible with: CX4 with PX4 Magazine Well Insert/Magazine Release, PX4 Full Size .40S&W, PX4 Compact .40S&W, PX4 Sub-Compact .40S&W* (Will extend below the base of the grip on a Compact and Sub-Compact)
JM4PX417 is an extended magazine.