Rimfire ignition began to supplant other American cartridge concepts by the time of the Civil War because of its simplicity of design and manufacture. Some officers carried Smith & Wesson .22 and .32 caliber rimfire revolvers as secondary arms. A few Union units armed themselves with Henry’s repeater (firing a .44 caliber rimfire cartridge) or the fast-loading Spencer repeating rifle (firing bullets of up to .55 caliber). Although not as powerful as the .58 caliber muzzleloaders carried by both Union and Confederate soldiers, the fast-firing Henrys and Spencers could produce a large volume of fire.
As percussion breechloaders were converted to accept true cartridges, those cartridges were mostly rimfire. The U.S. military issued rimfire cartridges as large as .58 caliber. However, there was room for improvement.
Early rimfire cartridges were prone to misfires. The priming compound was essentially glued into the rim cavity with organic binders. The only mechanical positioning came from the pressure of the powder charge against the fulminate. If handled roughly, a piece of the fulminate could fall out of the rim cavity, leaving a void and the potential for misfire. Another rimfire problem was that most cartridges were limited in power by the necessarily thin case. Thickening the case to handle more pressure also thickened the rim, causing misfires.