Detachable Box Magazine
Also: DBM · AICS Magazine
A removable box magazine, such as the AICS pattern, that swaps quickly and often allows a little more cartridge length.
A detachable box magazine is a self-contained magazine that drops free of the rifle and is replaced by hand, rather than being loaded one round at a time through the top. The AICS pattern became a near-standard in precision shooting, so an action cut for that footprint can run mags from many makers, and the bottom-metal or chassis is built to accept them.
The practical wins are speed and capacity: a shooter can reload in seconds and carry several loaded mags. Many of these magazines also offer a longer internal box than a fixed magazine, giving handloaders room to push the cartridge-overall-length out toward the lands. The contrast is a fixed floor-plate setup, which holds rounds internally and is emptied through a hinged plate.