Dating gun cartridges
This practice was primarily done on Remington revolvers, as their cylinders were easily removable and were held by a cylinder pin, unlike the early Colt revolvers which were held together by a wedge that went through the cylinder pin.
According to the Patent Office of the United Kingdom, "In the reign of Queen Anne, the law officers of the Crown established as a condition of grant that 'the patentee must by an instrument in writing describe and ascertain the nature of the invention and the manner in which it is to be performed.'" This gun's patent, number 418 of 1718, was one of the first to provide such a description. The square bullets were considered to be more damaging.
They would, according to the patent, "convince the Turks of the benefits of Christian civilization".
John Montagu, 2nd Duke of Montagu, Master-General of the Ordnance (1740-1749), purchased two guns for an ill-fated expedition in 1722 to capture St Lucia and St Vincent.
While shipping manifests state "2 Machine Guns of Puckles" (sic) were among the cargo that departed from Portsmouth, There is a replica of a Puckle gun at Bucklers Hard Maritime Museum in Hampshire.
If there is letter code, the first letter is always what I call the series.