Fort Craig was a U.S. Army fort that was established in 1853 as a protective outpost for the settlers and as a base of operations for continuing military campaigns against the Apache and Navajo. By the beginning of the American Civil War it had become the largest fort in the Southwest.
A few hours away was Fort Union Arsenal which in 1862 recorded having pinfire cartridges and guns in stock. Fort Union was the only major supply Arsenal for the whole area so it makes sense that the cartridges that were found around Fort Craig may have traveled through Fort Union.
The pistol cartridge that has been recovered from this location is one of the American made ones, procured by the Union Army, by Allen & Wheelock. The pinfire shotshells are various gauges by Eley Bros.