American Military Shoulder Arms, Volume 3: Flintlock Alterations and Muzzleloading Percussion Shoulder Arms, 1840-1865

Appendix III: Caliber Designations of American Military Shoulder Arms and Ammunition

Appendix III Caliber Designations of American Military Shoulder Arms and Ammunition Muzzleloading Smooth-Bored Arms In order to rapidly load a smooth-bored muzzleloading arm, especially one whose bore was fouled by residue from repeated firing in combat, the standard practice was to supply balls that were of smaller diameter than the bore in which they were used. These undersized balls were usually secured by wadding made up from the paper cartridge case, until the bore was foul enough to retain them in place. Until the early 19th century, the term “gauge” or “bore” was used to express the number of lead balls of a specific diameter in a pound. The higher the number of the “gauge,” the more the quantity of balls required to weigh a pound; therefore, the diameter of each was smaller. American .69 caliber muskets in the late flintlock period used balls of .635" diameter. The standard powder charge during the late flintlock period was 130 grains of musket powder. It was assumed that about 20 grains of the total 130 grains would be used in priming the musket’s pan. In April 1845, the secretary of war approved an ordnance board’s recommendation to increase the ball’s diameter to .65" for the Model 1842 musket. At the same time, the standard powder charge for musket ammunition was reduced to 100 grains, because the percussion system did not require priming powder. The charge for rifle ammunition was reduced to 75 grains. A package of ammunition was to contain 10 paper-cased cartridges and 12 percussion caps. Another Board recommendation , which was approved by the secretary of war, was the use of “pressed” balls: thereafter, until the adoption of jacketed bullets for smokeless powder arms, the lead balls and bullets were formed by swaging rather than casting, as this method of manufacture resulted in more uniform weights and diameters. Use of Buckshot: In close combat, or when firing at massed troops, the use of several round balls of .30" to .38" diameter each, instead of a single round ball, had a devastating effect. The buckshot was secured in the barrels of muskets by ramming its paper cartridge case over it, forming a tight wad. The first recorded American authorization for the use of buckshot ammunition was an October 6, 1777, order from general headquarters at Perkiorny that stated, “Buckshot are to be put into all cartridges which shall hereafter be made.” The use of buckshot ammunition, sometimes loaded with a single large ball and three smaller shots, continued throughout the smooth bore era, into the Civil War. For example, the state of Massachusetts received 100,000 buckshot cartridges, along with percussion-altered flintlock muskets, from the federal government in 1861. Appendix III 520 Muzzleloading Rifled Arms The .54 caliber flintlock and early percussion rifles used during the first half of the 19th century usually had a land diameter of .525" and a groove diameter of .540" to .545". These arms used a .525" diameter round ball. This undersized ball could be rammed down the barrel with a cloth or leather patch that would fill the bore’s grooves and, when fired, impart rotation to the round ball. A ball that was larger than the bore’s land diameter could not be rammed down the bore of a rifled muzzleloading arm if the bore became fouled from firing. In 1845, the powder charge was established at 75 grains of musket powder. The 1855 adoption of minie bullets and rifled muskets allowed an undersize sphero-conical bullet with a hollow base to be easily rammed down a rifled barrel from the muzzle. When the arm was fired, the expanding gas forced the skirt of the bullet’s base outward, so that it would engage the bore’s rifling, and have the rifling’s rotation imparted to it. Because the minie bullet’s base skirt filled the bore, most of the rapidly expanding gases were trapped behind it. This not only was far more accurate than smooth bores, but also resulted in higher ball velocities, with reduced powder charges. Following the introduction of the rifled musket using minie ammunition, the Ordnance department rifled, and rifled and sighted, several thousand existing percussion-altered flintlock and Model 1842 percussion muskets. The minie bullet for these .69 caliber rifled arms was .685" diameter, and weighed 730 grains. Because of this bullet’s superior ability to seal the bore as it...