Lets see if you can find that stamp? I dont think there is one the lock plate looks wrong, and the bottom sling loop is attached by a stud to the bottom the trigger plate instead of on the trigger bow, trailing edge looks pointed and the two examples I found on DGW dont quite look rite.
The top is a converted 1816
your ?? Gun
Like the Model 1816, the Model 1822 was a .69 caliber smooth bore flintlock, with a 42 inch barrel and an overall length of 58 inches. One of the most noticeable differences in the Model 1822 is the attachment of the lower sling swivel. The forward part of the trigger bow was provided with an enlargement which was drilled to receive the sling swivel rivet. Previously, the sling swivel had been affixed to a stud in front of the trigger bow.
Springfield musket - Wikipedia, the free encyclopedia