Gene - I have checked many current catalogs this morning for the major current manufacturers of .32 auto (7.65mm Browning) and found the following listed muzzle velocities for that caliber:
SAAMI 900 FPS
Geco 1000 FPS
CBC 906 FPS
Hirtenberg 984 FPS
MFS 1017 FPS
Fiocchi 1000 FPS
PMC 900 FPS
S & B 1043 FPS
PPU 901 FPS
Many of these have admonitions that they are either instrumental velocities from pressure barrels, or that they are taken under ideal conditions and that they may vary due to altitude, barrel elngth, temperature, humidity, etc.
My personal opinion is that out of a normal .32 auto pistol barrel few would exceed 1000 FPS under field conditions.
The high end of velocities you mention are for special loadings such as the French THV, plastic training bullets, etc. or for weapons specifically adapted to the load, like the Skorpion SMG or the Frommer Pistol (“Frommer Ladung” - Frommer Loading).
Of course, velocities are also higher for the hollow point .32s, most of which have bullets in the 60-grain range. My comments are all based on the 71 to 73 grain FMJ bullet.
Most, not all, .32 auto pistols are straight blowback in operation. Load levels are very important. The case velocity (sometimes called “case thrust” or “timing”) is very important. If the case leaves the chamber before the bullet has left the barrel, the case head becomes unsupported although still under pressure and can badly bulge or even burst, causing possible injury and certain damage to the gun. this “timing” is very critical in blowbacks and they are not tolerant of a very large spread of pressures and velocities like some locked-breech pistols are.
I found that when I started loading 9mm Makarov, before any supply of ammunition was available. Fortunately, I stopped increasing the loads as soon as I got the pistol to function perfectly. I was using shortend 9mm Para cases (not all together satisfactory, by the way, for many reasons) and cast .380 bullets not resized. In the absence of molds or bullets of proper diameter I gave up on it, as the loads were accurate when the still-undersized bullets took the lands, but very wild when they did not.
Some blowback pistols designed for “hot” loads compensate for this by heavier recoil springs or heavy slides, like the Astra 400, the Campo Giro, or in the latter case, the MAB PA-15. (As I recall, the MAB is not pure blowback, having a slight rotation to the barrel, but I could be wrong about that. It is certainly not a fully locked breech in the sense of the Browning tilting barrels, Walther style prop locks, etc.). The best example of trying to overcome the unsupported case head problem in a blowback pistol is the 9mm FAR, which has the solid head of the case lengthened so that even if part of it has left the chamber, it will not expand. The FAR has been covered on this Forum as I recall.
The point is, MOST 7.65 Browning ammunition is, even today, subsonic and I agree with Jean-Pierre that older loads were almost all subsonic, except perhaps the Frommer loadings. Erlmeier and Brandt don’t show the 17mm case Frommer (same as .32 Auto) as a separate round, but even the short case (13mm) round shows a MV of 1115 fps. By the way, even though a European book, E&B shows the average MV of the .32 Auto round as 984 FPS.
I believe, again, that the “X” headstamp was much more a matter of concealment of the manufacturing source, in case a case was left behind at an assasination, than a matter of identifying a special load for silencers. I could be wrong, of course, in absence of documentation of these rounds. The boxes are of no help at all - of course being anonymous, purposefully, I’m sure, for the same reasons the cartridge was. Just my opinion but based on some study done when I acquired my first variation of the “X” headstamp on 7.65mm (32 auto) many years ago. My first ones - I had four rounds, came out of the magazine of a WWII bring-back Walther PPK - no silencer provision - that had been loaded since that time. I acquired them circa 1966. I unloaded the pistol myself. The other rounds were Geco steel-cased rounds.