Welcome Triple Jack, and thank you for your courteous entry here, as well as being attentive to the 'rules' which are intended simply to prevent issues.
There is indeed a great core of knowledge here, which is dynamic as we all learn together by sharing information and experience. Many are more specialized in certain areas, so that is most helpful.
On that note, you mention air rifles, honestly I know even less on those than I do on regular firearms
so it might be good to see examples of these. It may sound silly, but these are the weapon form not BB guns correct? I know there were some type of guns using compressed air? even in Napoleonic times (an obscure article I saw).
Fernando was our Lead Moderator, who sadly passed away last year, and is deeply missed. He was an intent researcher and contributor on many topics especially when his interest was piqued in a specific area.
As has been noted by some of the guys here who know firearms well, the style of this example is typically regarded as from Sind regions, which are wide desert areas just below Afghanistan. These forms of course diffused widely with tribal interaction and trade of course extending into areas in Afghanistan. There are craftsmen who have assembled firearms faithfully for many generations, using components at hand, often from very old muskets and various firearms.
As noted, this example, like many of the guns out of these regions, is inherently valuable both ethnographically and historically. Its character suggests it was indeed a 'working' weapon. and its provenance from a shop in London suggests it may well have been an early souvenir from the notable British presence there from 1880s well into 20th c.
While often these guns were made to be sold as souvenirs though using genuine old components, many found as souvenirs came out of actual tribal use, as in my opinion this one may well have been. The key is to check the components, and viability such as alignment of touch hole and pan.
Old barrels from surplus guns were ubiquitous. The unusual star type rifling seems unusual.....what sort of round would be used is curious so I hope those with this knowledge might describe. The M1853 Enfield is noted, and these were popular in Afghan regions. The percussion (caplock) lock is from that period until I think c. 1880s?
Important note......conservation, not restoration on antique arms, just WD40 to stabilize and clean. Overcleaning destroys value.
Again, welcome and thank you for posting this,
Jim