The first U.S. Model 1840 Flintlock Muskets were produced at Springfield Armory in 1840 and the last were produced in 1844. A total of 30,421 were manufactured at Springfield Armory, while none were made at Harpers Ferry other than the twenty four 1835 dated Model Muskets.
At least 26,841 were altered to percussion at Springfield in 1851. It is documented that 1,000 M1840 Flintlock Muskets were issued to Pennsylvania in 1849 and 1,112 in 1851. In 1851, 87 were issued to New Hampshire. Only the muskets issued to New Hampshire have been identified thanks to the "NH" stamps on the left flat of the barrel at the breech. Of the 2,199 M1840 issued, currently only 19 are known in their original flintlock configuration with three in the Springfield Armory NHS Collection. Of the balance, all but two are marked "NH" on the left barrel flat.
There are a great many reconverted examples in collections and for sale on Gunbroker and Guns International.