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10mm Auto Once-Fired Brass
From Wikipedia: https://en.wikipedia.org/wiki/10mm_Auto
The 10mm Auto (10×25mm, official C.I.P. nomenclature: 10 mm Auto, official SAAMI nomenclature: 10mm Automatic) is a powerful semi-automatic pistol cartridge first developed by U.S. Marine Jeff Cooper and introduced in 1983 with the Bren Ten pistol. Its design was adopted and later produced by ammunition manufacturer FFV Norma AB of Åmotfors, Sweden.
Although it was selected for service by the Federal Bureau of Investigation (FBI) in 1989 from the aftermath of the 1986 FBI Miami shootout, the cartridge was later decommissioned (except by the Hostage Rescue Team and Special Weapons and Tactics Teams) after their Firearms Training Unit eventually concluded that its recoil was excessive in terms of training for average agents and police officers' competency of use and qualification, and that the pistols chambered for the cartridge were too large for some small-handed individuals.
These issues led to the creation of and following replacement by a shorter version of the 10mm that exists today as the .40 S&W, and while the 10mm never attained the mainstream success of this compact variant, there is still an enthusiastic group of supporters and users, and in recent years has started to grow again in popularity.
