Just to amplify on the proof marks as it is an important dating point. The marking of the barrels with the bore size, was a requirement introduced by the English 1855 Gun Barrel Proof Act and applied to both London and Birmingham proof houses. Prior to this date, i believe there was no requirement to do so, however maybe some makers did as there will always be exceptions to the rule?
The proof house chart in the post above was extracted from Diggory hadoke's book "Vintage guns for the modern shot" with grateful aknowledgement.