Here's what I've figured so far - Spiff called it a M1824, converted around the time of our Civil War. Neffi called it a M1822. Spiff got the model number wrong, but I'm guessing he meant the M1822, and based on the date on the barrel - he's correct about the conversion time - at least for when it was assembled into it's current configuration. Neffi got the nomenclature correct, if incomplete... but I'm having trouble finding good references, and the ones I did find, are not...