Beretta magazine well insert cx4 rifle px4 for 9mm/.40 mags FEATURES:-This magazine well insert for the Beretta Cx4 carbine will allow the shooter to utilize Beretta PX4 pistol magazines-The ability to use the same magazines in both the pistol & carbine is not only convenient, but also saves the shooter the expense of purchasing extra, model-specific magazines for the carbine-For 9mm/.40 Mags