First let me say that this is the only original muzzleloader double gun I have ever examined, so I may be mistaken about some things.
I looked over the barrels again with my magnifying glass and don't see any other markings besides the four proof marks. I measured the barrels again with my calipers. The right bore is .66 and the left bore is .68 so I guess it was originally a 16 gauge. I assume that at one time someone probably bored out the left barrel because it was pitted.
I have taken off the hardware and can not find a serial number anywhere.
There is nice engraving on every piece of hardware.
There are no cracks or chips in the stock. It appears to have the original stock finish which is worn a lot on the fore end, but not worn much on the main stock. It appears to have the original 16 point flat top checkering which is not worn much. Maybe it was not used much, or maybe at one time the stock was refinished and re-checkered. I think this gun was not used a lot but was neglected and allowed to get rusty too many times during it's life.
In my book "The Mantons: Gunmakers" they list two guns make by Joseph Manton with the lock signed Jos H Manton like on my gun. One is a flintlock blunderbuss made in 1832 and with no serial number. The other is a percussion double rifle with no serial number. I read someplace that back action locks first appeared around 1830, so thought this might be an original.
When I look at the details of how this gun was built, the craftsmanship is first class. The metal to wood fit is perfect. This is the first gun I have ever handled that I can do this; close my eyes and point the gun, then open my eyes it is right on. It fits me better than any other gun I have ever held.
However the gun is in poor condition. All of the steel hardware has been rusted so that it has lost the original finish and turned black, like a black patina. You can see a little of the charcoal blue on the locks, especially on the back side. The ramrod is old but not original. The bores were very dirty and rusted inside. You can see a little bit of the browned Damascus twist pattern on the bottom of the barrels, but the rest of barrels are so dark that you can hardly tell they are Damascus. Because of the dark patina, it is very difficult and in some places almost impossible to see the engraving that is on every piece of hardware. The nipples were rusted so badly that I had to apply liquid wrench twice a day for two days before I could unscrew them. Both locks have been poorly repaired and damaged. The left breach plug is not screwed in all the way. It's off by about 1/32 inch and that looks bad. All of the screws have been badly damaged from people using a regular screwdrivers on them. The under barrel lug has been replaced and there is solder showing all around it.
I bought this gun so I could have an original Joseph Manton gun to study and use as a model when building a new shotgun and for that purpose I think this is a good gun even though it was probably not made by a Manton. But I still would like to know who made it and about what year it as made.