Lew - the following information on the different internal base shapes of Canadian 9 mm ammunition comes from my article in the IAA Journal, Issue 429, page 27, entitiled “Defence Industries Limited 9 mm Parabellum Ammunition, Additional Information.” It is perhaps the shortest article I ever wrote - one page - amazing for someone as full of hot air as am I.
There is more in it than just that subject, so I will reproduce here only the paragraph relating to the subject at hand.
"Regarding serial production of this ammunition, with the "DI" headstamp normally encountered, some additional information might prove of interest. Bullet jackets were initially of Gilding Metal (non-magnetic). Sometime in 1942, Gilding Metal Clad-Steel jackets were used also. From 1943 on, all bullet jackets seem to be of the GMCS type. Three case designs were used during the life of the "DI" headstamp. The first two had the normal purple primer seal, sometimes so light they appear to be a mauve color, or not there at all. From 1942 to early 1943, cases had a flat internal base. From 1943 until some time in 1944, the internal base was flat, but with a concave into the primer pocker. Production was changed to a rounded internal base in 1944, and this last type had a green primer seal for identification. Early 1942 production of ball cartridges had a heavily cannelured case, like the "DC 42" rounds, but the cannelure was eliminated that year, and production cartridges from the latter part of 1941 and after have a smooth case. Cartridges have been disassembled and have confirmed this information. (Note added while typing this copy on this forum: This last sentence seems out of
order, and should have been right before the sentence about case cannelures) Primer cups were usually brass, but cartridges can be encountered with nickeled cups. A specimen dated “42” is at hand and has the normal triangular primer crimps. These are not reloads."
Hope this answers the question. This information first came to me from John Belton, long before I added it to some information about the “DC 42” headstamp to make up a usable article for IAA. My information from John was in response to a question in the Cartridge Trader issue of 239, and was contained in a personal letter to me from John, dated 25 December 1975. I don’t know off-hand if he related the information also to the Cartridge Trader then, or if I passed it on. I have no copy of anything written by me at that time in my files.
We discussed this sometime around then, and also, I remember clearly, about the time I wrote the article late 2002 that appeared in the January/February 2003 Journal.