[Raf]

I agree but if you look at the relationship between the GP and the crown on the 1702 version the crown is considerably larger than the GP and on my version it is the other way round . I never know how literally we should take these things as published marks are presumably taken from dated examples and proof stamps must have had to be constantly re - made . I cant imagine engravers going to great lengths to ensure stylistic consistency. My argument for a seventeenth century date is simply the thing has a restoration feel about it . By the end of the century English gunmakers had evolved a more austere and confident approach based on elegant lines and sound craftsmanship . Having said that there were plenty of continental gunsmiths working in London at the turn of the century so maybe that accounts for the decoration.

Yes the barrel does turn off

The Worshipfull Company of Gunmakers was incorporated in 1637 and consisted of 125 gunmakers responsible for proving and marking all types of guns both English and continental and for enforcing regulation. Proof firing was carried out by individual gunmakers on their own premises although a collective proof house was established in Whitehall in 1715 . Therefore prior to this each gunmaker must have had their own version of the crown / GP stamp .

On the subject of proof marks / makers marks in general here is a selection that might be useful for reference .