Small arms were commonly designated by their caliber, method of loading (breech or muzzle), and manufacturer. The most frequently used small arms in both the Union and Confederate armies were the .58 caliber Springfield musket and the .69 caliber Harpers Ferry rifle. Both were muzzleloaded weapons that fired the Minie ball, a revolutionary hollow-based bullet that greatly accelerated the loading and firing process.

The increased use of these weapons resulted in a remarkable change in infantry tactics. Smoothbore muskets were notoriously inaccurate and had a relatively short range; firing lines as close as 100 yards inflicted little damage. For maximum effectiveness, soldiers usually had to run toward the enemy firing en masse and hoping they hit something, then use their bayonets for close-quarter fighting.

The rifled musket introduced just before the Civil War was a completely different weapon, however. It offered accuracy at a considerable distance; skilled snipers could hit their target as far as a half mile away. This accuracy made a frontal assault especially hazardous. Unfortunately, many commanding officers failed to take these new weapons into consideration when formulating battle tactics, resulting in a huge number of casualties.