As much as I don’t mine helping to identify Antique weapons and such, it is hard without something to go one. Just to list a few things that can help some of us to identify a weapons are but not limited to,
1. Any markings on the weapon (serial Number, Lock Makers name).
2. Caliber, or Gage, (bore size if Caliber or gage is unknown).
3. Photos of the weapon, (top, bottom, left, right, front, and back sides).
4. Any other markings that are on the weapon, (sometimes symbols were used by the makers of the weapons).
Double barrel shot guns, may lack many markings that rifles and pistols have but there will always be something some place on the weapon. One such place that may hold a mark can be the face of the chamber end of the barrel, just break it open and have a look see if there is something there.
Don’t be afraid to use a magnifying glass to look real close for marks sense many old weapons may be warn or obscured by pitting. Oft times this will be cause for over looking the signs of markings sense it makes it look as though it is part of the pitting instead of actual marks.
In some cases of double barrel shot guns of one can gage the chambers of both barrels with a id mike or a good machinist ruler, you may find that one is slightly bigger then the other. This was a habit of one gun maker a long time ago and helped to identify that shotgun.
All flint lock’s and percussion weapons have some form of a lock, and someone made that lock. Many gun makers used others locks along time ago and that lock maker most times put their mark or name on it someplace. Most were marked on the out side but some may of marked the lock in the inside so you might have to remove the lock from the weapon to have a look see.
In some cases the maker of a weapon made just one of a kind, and may of not marked anything on the weapon at all. Note that markings were not required for many years, this had more to do with latter day laws requiring some form of markings from the maker to be put on the weapon.
Anything is of a help, but don’t get your hopes up to much with antique weapons sense not a lot of records were kept and with a one of a kind nothing is out there to go by.