That is a Nepalese 3rd Model Bess musket. I can just barely see the remnant of the crest where the British Crown would be on a British musket, or the lock maker name on a [British] East India Tea Company musket. The Nepalese engraving would vary from a temple, a crest, or in some cases an elephant is found but there is a debate about the elephant possibly being a more recent thing for tourist sales.... who knows....
. IMA sold hundreds of them over the past decade or so, and still offers some for sale, bought from Nepal. After the British went to caplocks, a lot of BEITC muskets and Crown muskets were sold off. Could that have been sold by Nepal to somebody in Afghanistan in this century? Sure. Could that have been in Afghanistan when the British were mucking about? Sure. (In fact it might have been used by British Army or Indian provincials). Last time I checked there was no way to tell when the Nepalese got each musket and put it into storage.
LD