The original Glock factory magazine made of high-tech polymer with a hardened steel core for highly dependable sidearm feeds even after extraordinary use. Trust the best when it comes to ensuring your Glock pistol is ready to perform. NOTE: GLOCK MAGAZINES CAN BE VERY DIFFICULT TO LOAD WHEN NEW. OFTEN THE LAST ROUND WILL NOT FIT UNTIL THE MAGAZINE HAS UNDERGONE A BREAK-IN PERIOD. IT IS RECOMMENDED THAT THE MAGAZINE BE LOADED WITH ALL BUT THE LAST ROUND AND LEFT FOR A FEW DAYS TO COMPRESS THE SPRING. CYCLING THE MAGAZINE FROM FULL TO EMPTY MULTIPLE TIMES CAN ASSIST IN THE BREAK-IN PERIOD.