Hi Anandalal,
Thank you so much for your input!
When surmising a Cingalese-Malayan stylistic influence I let myself inspire by Rainer Daehnhardt's book on the close connection between Portugal and those countries. As you know I know almost nothing about weapons from Sri Lanka or Malay.
On the other hand, I cannot find any Western European art style on that piece either. My first thought when looking at that winged figure of Justice on the buttstock was the Inca culture in Peru but that's impossible.
I attach two Cingalese guns scanned from Howard L. Blackmore:
Guns and Rifles of the World, 1965. Don't the running scrolls on the lower buttstock look similar to those on the Coburg gun?
Maybe somebody else from the Ethnographic forum can help us?
Best,
Michael