text: Rim fire and center fire refer to the location on the cartridge where the priming compound is located.  In rim fire shells such as the .22 rim fire, the priming compound is located in the rim of the base of the shell.  The gun which is chambered for these shells have a firing pin which strikes the rim of the shell thereby igniting the priming compound.  With center fire shells, the priming compound is located in a primer which is pressed into the center of the base of shell.  Guns chambered for center fire cartridges have the firing pin located so that it strikes the primer located in the center of the base of the shell.  Most cartridges are of the center fire type.