Can we rule out a recent import from the Nepal Cache from IMA?
Well it could possibly be from there but seems unlikely. Actual British built pieces were few and far between in the Nepal cache Enfields and this has the proper markings of a British built rifle. A few locks have shown up mated to Nepal made barrels. Complete British made rifles have been mainly later unmentionables. The only complete muzzle loaders of European origin that showed up were East India Company smoothbores that predated the Rifled Musket and a handful of various other guns (some pistols, carbines, a couple sporting rifles) that were sorted out to be sold at a premium price.