A magazine for a firearm includes an elongated containing body and a
closure member adapted to hold cartridges. The closure member
longitudinally slides on the containing body and is extendable to open a
side of the containing body for cartridge loading. The closure member has
opposing sidewalls forming an integral handle surface that can be grasped
for moving it. A follower and spring bias cartridges toward one end of
the magazine. A latching mechanism is provided for holding the follower
in a disengaged position when the closure member is extended, and is
configured to release when the closure member is closed. Preferably, the
containing body and closure member are constructed to include integrally
formed features that cooperate with an automatic latching mechanism, thus
minimizing parts.