From the web:
For the Silver Jubilee of King George V in 1935, James Purdey & Sons presented His Majesty with a miniature pair of hammer ejector guns, nos. 25000 and 25001. Built to exactly 1/6 the size of the king's pair of 12-bore guns, the fully working miniatures were supplied with fully functioning ammunition. The cartridges were .47 inches long, .18 in diameter and loaded with 2.02grns of dust shot. It is said that the cartridges cost as much to produce as the guns themselves. The guns and a complete box of 25 cartridges are preserved in the Royal Gun Room at Sandringham.