Greener perfected choke boring in 1874 and in June 1875 it was widely publicized by "The Field" trial. Shortly thereafter, UK changed its proof laws to require "Not For Ball" on barrels with chokes. Here is an example of where the stamp should be placed from Diggory's recent article:
A gentleman in UK recently contacted me through Diggory and forwarded photos of a gun I didn't have, 20740
- firmly dated per the chart to 1877. The problem is. - no NOT FOR BALL stamp. It is choked - probably using Greener's technique so the barrel was unlikely to have been proofed pre 1875 and then used in 1877.
I started researching this in my database of Reilly9's. I can find two dozen extant Reilly shotguns from summer 1875 forward - two advertisements mention a NOT FOR BALL stamp. But there is not one photo of the stamp until one gets up to 24534
(1882), one of Cyril Adams' 12 bore pigeon guns:
A lot of auction houses do not publish photos of the barrel flats...admittedly...but there are enough photos from this time period that some sort of stamping NOT FOR BALL should have been recorded. Is there any explanation for this.