Lew - the real question here is whether or not a Model 1911/1912 Steyr-Hahn will accept both .38 Auto. The Steyr is a very well made pistol held to good tolerances. I cannot say that they will not accept .38 ACP rounds because I have never tried it (being semi-rimmed, the .38 ACP/
Super was outside of the parameters for our book on the 9 x 23 mm Rimless cartridges). However, published dimensions show the base dimensions of the two cartridge have an overlap of dimensions, so some .38 ACP rounds might fit, if they were not maximum dimensions. The .38 ACP OACL is slightly shorter than that of the 9 mm Steyr, and that might cause some headspacing problems in a barrel that was not specifically designed to accommodate a semi-rimmed cartridge case. Also, as mentioned before, I do not recall the breech face configuration on the Steyr pistol; that is, whether or not it would accommodate the .38 ACP semi-rim (0.400" to 0.407" head/rim diameter as opposed to Steyr dimensions of 0.376" to 0.383 inch, a very large difference).
Maybe if one of our members has a good condition Steyr Hahn and could carefully try chambering both caliber cartridges (preferable inert rounds, for safety’s sake), we could get a better idea.
My belief, by the way, is that the Spanish marking on some pistols “9mm/.38” is simply a joint metric/inch designation for the 9 mm Bergmann/Bayard cartridge. Despite the common opinion that it means “9 x 23 mm BB/.38 ACP” I have found no solid documentation for that belief. I mentioned, perhaps in another thread (couldn’t find it here) that both Hungary with the spurious Geco box, and Germany, specifically on boxes of blanks, refers to the 9 mm Parabellum cartridge also as the “.38 Luger,” another use of the metric and inch measurements together, although the latter designation is not used in any “inch-measurement countries” of which I am aware.
I spent some time in both of Antaris’ books, the one on Astra pistol and the one on Star pistols, and found no satisfactory explanation for that marking. I note, though, that some pistols made in Spain in 9 mm Corto caliber were marked “9 mm/.380 Auto” with the 9 mm, of course, referring to the 9 mm Short. That marking is clearly a case of nothing more than give both the metric and the inch designation for the SAME cartridge.
I would welcome any documentation on the marking “9mm/.38” found on Spanish pistols, as it is a question that has been argued and puzzled over all of my gun and cartridge collecting life. Perhaps some of our Spanish members could provide an absolute answer. I do not pretend to be convinced that my own opinion of the marking is correct - I think it is, but that thought is not etched in stone. The biggest factor for me is the “9 mm/.380” marking, which clearly is two designations for the same cartridge.
I would never, never fire a 9 x 19 mm cartridge in a pistol chambered for a 9 x 23 mm cartridge. Most competent authorities would agree, but unfortunately, you still see the old myth of, for instance, the Astra 400 being able to fire .380 auto, 9 mm Browning long, 9 mm Parabellum and even once in awhile, .38 Super, which is pure insanity. I would not even attempt to fire .38 Auto in a Steyr (if it fit) or an Astra 400, as the case is shorter than the Steyr or Bergmann-Bayard round, and the in the case of the Astra, the fit of the rim in the breech face is not correct. Some, with sloppy dimensions, will accept the semi-rim, but this is not by design.
Edited to add comments and to correct on spelling error