Polymer firearm magazine width retention system

A double stack magazine for a firearm comprising:

• a tubular magazine body formed of polymer, the magazine body defining a vertical centerline and an internal cavity configured to hold a stack of cartridges, the magazine body including an at least partially open top end for dispensing cartridges, a bottom end, a front wall, a rear wall, and opposed lateral sidewalls extending between the front and rear walls;
• the magazine body including a lower double stack section configured to hold a vertical staggered double stack of the cartridges, an upper single stack section, and a transition section formed between the double stack section and the single stack section;
• a magazine spring disposed in the cavity;
• a follower moveably disposed in the cavity and biased in an upwards direction towards the top end of the magazine body by the magazine spring, the follower configured to support and dispense cartridges in the stack from the magazine;
• a U-shaped metallic retention clip coupled to the rear wall and both sidewalls of the magazine body at a midsection of the magazine body between the top and bottom ends, the retention clip configured and arranged to restrain the magazine body from bulging in a lateral direction at the midsection when cartridges are loaded into the magazine.

A method for preventing bulging of a double stack ammunition magazine for a firearm, the method comprising:

• providing or having the magazine which includes a polymer magazine body, a partially open top end, a bottom end, and an internal cavity comprising a lower double stack section and an upper single stack section;
• installing a spring-biased follower in the internal cavity operable to dispense cartridges from the magazine;
• coupling a metal magazine shape retention clip to a midsection of the magazine body before or after installing the spring-biased follower;
• and
• loading cartridges into the internal cavity onto the spring-biased follower until a stack of cartridges extends from the upper single stack section at least partially down into the lower double stack section of the magazine;
• the shape retention clip providing a resistance force onto the magazine body opposing outward acting forces thereon created by loading the cartridges into the double stack section, the shape retention clip preventing outward bulging of the magazine body at the midsection.