The GLOCK G27 magazine is constructed from a hardened steel insert encased in high tech polymer to protect the magazine and prevent deformation even when dropped from a great height. The high quality spring and follower ensure reliable feeding from the first round fed by a fully compressed spring down to the last shot. Its double cut magazine body also works with a reversed magazine catch on Gen4 and Gen5 GLOCK pistol models.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.