I am sure Mike O'Donnell's book on Gettysburg relics has more to say on them, but I do not possess that book. I do have The Illustrated History of American Civil War Relics, an earlier book of his and Steve Sylvia's. On pages 106 and 107 these engraved pieces are shown and one of the captions (page 106) says that "the manufacture of these engraved battlefield souvenirs began around 1870."
They are still highly prized by some collectors. Because the work was done so close to the war's end, the condition of the projectiles is usually very good.
The stencilling on the Mullane ties it to the Danner Museum also. I think you have a cabinet card showing shelves full of these projectiles, numbered similarly. I understand that these were sold off the shelves and replaced as best as possible with a similar style shell with a stenciled number on it which in turn could be sold. I have a partial one (half a 3in Schenkl case shot shell shown below) I got for a small amount at a relic show, but these too go for big money to some.
Here is a poor image of one of these Danner Museum cabinet cards:
http://jamesdjulia.com/auctions/327/images/lrg/70018x9.jpgAlso, the reconstructed canister only has 25 balls, 2 short of what it should.
