A magazine doubler includes a resilient body with two cavities each having upstanding ribs to carry magazines therein at different heights. A bracket and spaced screws are mounted medially between the front and back of the body to squeeze the body to generally conform it to carried magazines therein. A blocking element is used to replace the top round in one magazine to prevent the upper round from being dislodged during use of the doubler. Such element is tethered and biased by a rubber band looping around one of the screw shanks.