A Rare .65 Artillery (?) Flintlock Service Carbine

A Rare .65 Artillery (?) Flintlock Service Carbine
Late 18th Century
With sighted barrel, slightly rounded lock engraved with 'GR' crowned and 'Tower' on the tail (jaw-screw replaced), walnut full stock, the butt with storekeeper's mark dated '1790', and deeply carved with 'ER' crowned, full regulation brass mounts, and iron ramrod (sling-swivels removed, ramrod shortened, some wear and pitting), Ordnance view and proof marks
37in. (94.5cm.) barrel