I am not that, this gun was ever flint. There is no sign of pans and the locks fet under the barrels, where on a flint they are more to the side. There is also no sign of frizzen or frizzen spring attachment. Unless the locks were engraved after the conversion, the engraving and maker name would have been covered up by these attachments. The Nock and Manton style breechs did have a narrowed breech plug, to bring the locks in narrower, but it still reguired the locks to have the pans to the side of the breech. The "L" shape of the lock where it fits around the flash guard and up under the barrel are very typical of percussion locks. The plugs you see are pretty common to quality percussion guns and are called "blow out plugs" by many people. The equal length triggers are very uncommon to flint guns, as the front trigger is usually about 1/2 length. The trigger guard is not a larger loop, but one that is typical of percussion guns.
The hammers though are sure unique. It is as if the nose of the hammer is adjustable.