Why not at all! I got it from "Harper's Ferry Armory and the New Technology; The Challenge of Change" by Merritt Roe Smith , published by Cornell University Press, 1977.
This is a heavily researched book with many sources, but as with any book, it is possible that the entry was a typo or there was a mistake in the original records. The table is highly detailed and quite complete covering the years from 1801 to 1860. It includes figures for each year the following applicable items:
Flintlock Muskets, Percussion Muskets (M1842), Rifled Muskets (M1855), Flintlock Rifles (M1803/14), Percussion Rifles (M1841,M1855), Pistols, Pattern Arms, Verifying Instruments, Miscellaneous Products, Accoutrements, appendages and extra parts, Alterations and Repairs, Output in Musket Equivalents, Number of Production Workers, Output (musket equivalents) per production worker, Ordnance Dept. estimate per musket and Writer's estimate of cost per musket in Dollars at Harper's Ferry. It appears that the table was compiled by the writer from data gathered from three primary sources. Those sources are:
American State Papers: Military Affairs (2:481; 5:913-923)
Ordnance Reports , Stephen Benet (2:230)
Annual Reports of the Secretary of War in the Congressional Serial Set.
He said in the footnote that where possible, the figures were checked and verified with the appropriate archival records of the Office of the Chief of Ordnance (OCO, entries 5, 21 and 1003).
I know that is a lot of stuff, but if you want to research the history of your musket, you need all the info you can get. I'm not sure how to get in touch with the proper people to read those sources.
I know how you feel about getting hopeful that you have something rare or special and getting let down. Been there. All I can say is, the table in the book shows only one M1855 RM made in 1857 along with 10 M1855 rifles and 1 Pattern rifle. If I find any new info I will let you know. I personally would think that more than 1 rifle musket would have been made that year and that possibly records showing that may have been lost when the arsenal was burned. Regardless of that, I feel that there wouldn't be very many of them in existence because the number made was probably small to start with and a good number may have been among those destroyed in 1861. I hope you get good news about your musket and you get to enjoy it for a long time.
:thumbsup: