55 Boys & .5 Vickers "Swirl Paint" on ctge

Peter White has these two cartridges which have been painted with a swirl pattern. The cartridges were acquired over 40 years ago from separate sources. The question is "what is the significance or reason for the painting. The Boys WII has the normal dark green primer annulus while the Vickers SAP has no or clear annulus colour. Speculation?



The use of paint on British cartridge cases is unusual (there are exceptions), as Silver nitrate is the preferred method of marking. With paint it is hard to regulate the thickness, prevent runs etc., it will invariably melt in a hot chamber and lead to stoppages and last but not least the residue can catch fire.

The only reason I can think of is that someone had too much time on their hands & these got separated before Peter acquired them.

Not having an answer or even something close to a clue but could not resist showing this one:


Peter White says that the 55 Boys has the appearance of stannic staining while the .5 Vickers appears as chemical staining.

Either way, easy to do with a wrap of adhesive tape before staining. Neither look like factory efforts. Some documentation would be necessary to provide proof.