This is a original Park Rifle with no replacements built approximately 1850 by Gasqoine & Dyson of Manchester , Lancashire UK their business was at 1 Blue Boar Ct 1846-1852 then 26 Market Pace 1854- 1864
The measurements of the octangle Damascus barrel is 1 inch at the breech and tapers down to 7/10 inch at the muzzle
Feltwad