After doing a little research I find a few things that don't look right such as the long breach plug tang and only US stamped on the Lock. This gun obviously started life as a flint Lock and was converted to percussion with a drum and nipple both missing. The gun was also shortened some amount, any marking forward of the hammer that may have been on the lock may have been removed during the conversion, but no date and only US stamped at the rear of the lock confuse me. Any thoughts on what this gun may be.