The nickel-case SBP 9 mm Luger round, with black PA, which I also have in my own collection, falls right into line with a .38 AUTO round also made for S&B in México. It too has a nickel case, nickel boxer primer and a black primer seal. The bullet is GMCS FMJ RN. However, in the instance of the .38 AUTO, the total headstamp is that caliber marking at the bottom of the cartridge head. It is anonymous as to the case maker on the cartridge itself. There is simply no entry other than the caliber.
To help put these cartridges into a time frame, I acquired my .38 AUTO version in April 1972, on my first trip to Europe. I saw it in the collection of Manfred Beutter, during a visit to his house in a town very near to Obendorf and the Mauser factory, which we visited that morning. I had gushed a bit over the cartridge, and before we left the house, Manfred told me that the caliber was of little interest to him and he gave me the cartridge. Our friendship, by the way, lasted for over 40 years, ending only with his passing a year or so ago. One of the best aspects of our hobby, of course, is the lifetime friendships made through participation in it.
Manfred seemed to imply he had had the cartridge for at least a couple of years, putting it in line with Lew’s comments on his 9 mm Para round.
There is another interesting .38 AUTO round. The caliber markings are nearly identical to those of the known Mexican-made round for S&B, but it also has the DOMINION brand name at the top of the head of the cartridge. The case is nickel and the primer seal is black, the latter feature being very unusual for Dominion commercial ammo, even of the 1970s.
The big difference between the two .38 AUTO rounds mentioned is that the one known to be made in México for S&B has a GMCS bullet, while the similar DOMINION round has simply a GM bullet. The 9 mm Para round covered here by Lew has a GMCS bullet too. In my entire collection of auto pistol rounds, I cannot think of a single Mexican-headstamped cartridge of any caliber that I have that has a magnetic bullet. I checked my catalog in calibers 9 mm, .38 AUTO, and .45 AUTO, and that proved true, regardless of the date of manufacture. That leads me to believe that those two rounds were perhaps loaded by S&B. If the black PA DOMINION .38 AUTO case was made in México it could have been sent to Canada as loaded ammunition, or since Canadian commercial rounds are virtually always with GM non-magnetic bullets, loaded in Canada. That is, if there is a Mexico-Canadian connection at all, since we have no documentation of the Canadian round with characteristics similar to the Mexican-made S&B rounds. Only headstamp and and primer features.
It is only fair to state that the rim thickness, and shape and sizes of the extractor groove and extractor-groove bevel vary quite a bit between the DOMINION-Marked round and the cartridge for S&B. Perhaps one of our Canadian friends has a box for the nickel-case DOMINION .38 AUTO rounds and can check it for nationality markings?
(NOTE: There is also a nickel-case 9 mm Para round from Dominion, but all of the characteristics of that cartridge, including its red PA, seem to be correct for Canadian manufacture.)