I think a double-barrelled coal-burner is probably the antithesis of Mr. Khan's vision for a cleaner London.
On topic, I picked up this snippet from another forum, but have yet to read further on the matter:
"Shortly before the B'ham proof house opened, in 1813, there was a piece of legislation introduced in Parliament, sponsored by the London gun trade. It required that all barrel markings denote where the barrel was actually made - which would have ended the custom of putting "London" on B'ham made barrels. The legislation went absolutely nowhere when the B'ham makers pointed out that virtually all of the London makers were buying their barrels semi-finished from B'ham, finishing them and having them proved at the London proof house... so even the "real" London barrels were B'ham products.
https://americanlongrifles.org/forum/index.php?topic=15087.0"
If the above is accurate, perhaps it might help frame a date for the gun.
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