Springfield Model 1842 The US Model 1842 Musket was a . 69 caliber musket manufactured and used in the United States during the 19th Century . It is a continuation of the Model 1816 line of muskets but is generally referred to as its own model number rather than just a variant of the Model 1816 . The Model 1842 was the last U . S . smoothbore musket . Many features that had been retrofitted into the Model 1840 were standard on the Model 1842 . The Model 1842 was the first U . S . musket to be produced with a percussion lock , though most of the Model 1840 flintlocks ended up being converted to percussion locks before reaching the field . The percussion cap system was vastly superior to the flintlock , being much more reliable and much more resistant to weather . Like all Model 1816 derivatives , the Model 1842 has a . 69 caliber barrel that was 42 inches in length . The Model 1842 had an overall length of 58 inches and a weight of 10 lbs . A great emphasis was placed on manufacturing processes for the Model 1842 . It was the first small arm produced in the U . S . with fully interchangeable ( machine - made ) parts . Approximately 275 , 000 Model 1842 muskets were produced at the Springfield and Harper ' s Ferry armories between 1844 and 1855 . Model 1842 muskets were also made by private contractors . However , these were few in number . Some were made by A . H . Waters and B . Flagg & Co , both of Millbury , Massachusetts . These were distinguished by having brass furniture instead of iron . A . H . Waters went out of business due to a dearth of contracts in New England , and Flagg entered into a partnership with William Glaze of South Carolina . They relocated the machinery to the Palmetto Armory in Columbia , South Carolina . Instead of “ V ” over “ P ” over the eagle ’ s head , these guns were usually stamped “ P ” over “ V ” over the palmetto tree . Most of the output of the Palmetto Armory went to the state militia of South Carolina . There were only 6 , 020 1842 type muskets produced on that contract and none were made there after 1853 . Like the earlier Model 1840 , the Model 1842 was produced with an intentionally thicker barrel than necessary , with the assumption that it would likely be rifled later . As the designers anticipated , many of the Model 1842 muskets had their barrels rifled later so that they could fire the newly developed Minié ball . Tests conducted by the U . S . Army showed that the . 69 caliber musket was not as accurate as the smaller bore rifled muskets . Also , the Minie Ball , being conical and elongated , had much more mass than a round ball of the same caliber . A smaller caliber Minié ball could be used to provide as much mass on target as the larger . 69 caliber round ball . For these reasons , the Model 1842 was the last . 69 caliber musket . The Army later standardized on the . 58 caliber Minie Ball , as used in the Springfield Model 1855 and Springfield Model 1861 . Both the original smoothbore version and the modified rifled version of the Model 1842 were used in the American Civil War . The smoothbore version was produced without sights , as they provided little value to a weapon that was only accurate to about 50 to 75 yards . When Model 1842 muskets were modified to have rifled barrels , sights were usually added at the same time as the rifling .