A magazine assembly for a firearm in one embodiment includes an outer magazine housing configured for attachment to a firearm and a magazine removably insertable into the housing. The magazine includes an axially extending internal cavity configured to hold a plurality of ammunition shells in stacked end-to-end relationship. In one embodiment, the magazine has an elongated tubular body. A shell catch lever is slideably mounted on the magazine for linear and pivoting movement in one arrangement. The shell catch lever retains a shell in the magazine in a first lateral position and releases the shell from the magazine in a second lateral position. The shell catch lever operates to retain and release shells from the magazine when either removed from or positioned in the magazine housing for loading the firearm.