Hi,
Believe it or not, I think the same gun is pictured in John George's book on English guns and rifles published in 1947. He dates it to the English Civil War period so I guess there is a lot of uncertainty about when it was made. Robby, the dog serves as a safety for half cock (some locks had no half cock notch just the dog) and drops back when the cock is pulled to the full cock position. The barrel is loaded by unscrewing the plug, pouring in the powder and then dropping in a ball. The screw is replaced and the gun primed and fired. The ball fitted tightly in the bore to make a gas seal like a modern bullet. Thus, the gun shot accurately and delivered a lot of knock-down power. They were slow to load; however, for deer hunters, they offered the advantage of loading while lying down and killing at great ranges. That is also why they were popular during the ECW for sniping. There are stories of English officers (parlimentary and royalist) being gunned down by hidden shooters just like during our Civil War. The muzzle ring serves to strengthen the muzzle but perhaps more importantly, it serves as a sight ramp. Look at the severe swamp in the barrel and you can see how it would need a very high front sight to compensate for the taper. If my books are accurate and the gun is the one pictured, it should be 12 bore with well worn rifling. According to George, the chamber had the capacity for 6 drams (165 grains!!) of powder, however, he does not say if that included the bullet. The barrel wall thickness must be pretty thin near the muzzle, hence the reinforcing.
dave
