MagBlok is like a rimless 1/2 dummy round that goes into your magazine like a normal cartridge but due to its shape it will not feed into the chamber. Thus by pushing the magazine follower down it tricks your firearm into acting the same way it would if you had a magazine fully of ammunition but without the hassle of cleaning up dummy rounds during your dry fire practice training session! MagBlok is included with the purchase of BarrelBlok or can be bought on its own.