That would be my guess, although it could have been the M1840 (aka M1835) - 30,421 produced in '49-'51 with 26,841 converted to percussion in '49-'51, and more altered at a later date. Conversions occurred all the way into the late '60's.
Of all the flintlocks held in the National Armories (>700K) by 1848, everything made prior to 1812 was considered unserviceable and not worth repairing, so that rules out almost everything made prior to the M1816 except for the M1814, which is unlikely since only 2K were produced and sold to individual states.