Nice! An educated guess; and fairly certain in what I believe and I strongly believe that it is the work of The Midland Gun Company of Birmingham and based on their model of the 'Demon' hammer gun. The 'R' on the underside of the barrels looks to be the mark of one of the Rees brothers who worked for M.G.C. as a barrel borer. The standard 'Demon' was a 12 bore but other bores could be ordered. The lock-up shown was of that model and although they had stock catalogue items they would mix and match to customer requirements. I'm a good 95% on my assertion. Hope that helps. Lagopus.....
