Has no maker mark but has British proof marks under the barrel. Crown CP (final black powder proof for the smooth bored muzzle loader barrels. There is a crown over V, which is a final view mark for proof. Barrel length is 5 3/4" and overall length is 11". Caliber is .45 and barrel is smoothbore. Very unusual underhammer as the cocking knob is a better design so you can grasp it easier and the rim is knurled. The trigger guard is large and different design from other underhammers. The bag shape grips has a provision to attach a shoulder stock. We have searched Herschel Logan's book Underhammer Guns and did not find anything like this pistol. This is very well made and probably over built. If you collect underhammer pistols you don't have this one! Note: our wizard of a French gunsmith can make the shoulder stock and attachment fitting if the buyer wishes. Stock and fitting at additional cost of course.