A non-detachable magazine lower receiver for a firearm includes a stock mount, a trigger well extending from the stock mount, and a magazine well. The trigger well is configured to receive a firing mechanism. The magazine well is configured to receive a magazine. A proximal wall of the magazine defines a retention opening that passes through a distal wall of the trigger well. The retention opening is configured to receive a magazine retention member for fixing a magazine recovered in the magazine well to the lower receiver.