What constitutes a load so different from the usual as to be described as a “special load” is of course a matter of opinion. I should perhaps explain that I kicked off this discussion on my forum because I was curious about the ballistic performance of the 9 x 25 compared with the 9 x 19, especially when loaded up to give maximum performance in an SMG. I was primarily interested in the muzzle energy developed rather than in the type of bullets or case materials.
For the sake of comparison, the military 9 x 19 2.z ammunition fires a 115 grain bullet at 1300 fps (7.45 g at 396 m/s) giving 434 ft lbs (585 Joules), but the powerful Hirtenberger L7A1 NATO SMG loading fires a 124 grain bullet at 1300 fps (8.04 g at 396 m/s) from a 4" barrel, increasing to an average of 1444 fps (440 m/s) from SMG barrels of 8-10", giving a muzzle energy of up to 577 ft lbs (778 J).
Various contributors responded, quoting bullet weight and muzzle velocity figures for the 9 x 25 Mauser from a variety of sources. One difficulty is often in determining the barrel length used to make the measurements. Where this is quoted, commercial loadings generally used the 5.5" (140mm) barrel typical of the Mauser C96 family. Anyway, the outcome of my little survey is this:
First, the bullet weights. The standard weight quoted is usually a 127 or 128 grains (8.2-8.3 g) military ball type, although Erlmeier/Brandt quote three different bullets: FMJ ball at 123-128 grains (7.97-8.30 g); soft-point at 132-133 grains (8.55-8.65 g); and a flat-nosed soft or hollow-point at 136-139 grains (8.8-9.0 g). They also quote a muzzle velocity of 1361 fps (415 m/s) from a 5.5 inch (140 mm) barrel without specifying which bullet weight this applied to, but as they give a muzzle energy of 522 ft lbs (703 J) we can calculate the bullet weight to be 126 grains (8.16 g). The only significant variation in military bullet weights I have encountered are the two “special loadings” already mentioned for the 39/43M in Thompson’s article: 156 grain ball and 139 grain AP.
Second, the muzzle velocities. COTW lists the 9 x 25 factory load as 128 grains at 1362 fps (8.29 g at 415 m/s), while Military Small Arms quotes 128 grains at 1350 fps (8.29 g at 411 m/s). Barrel length not specified, but I suspect this is probably 5.5". A German commercial loading is quoted as 127 grains at 1325 fps (8.25 g at 404 m/s) from a 5.5" (140 mm) barrel, at a chamber pressure of 35,500 psi.
Figures from various sources quoted for 9 x 25 SMGs include the following:
Steyr-Solothurn S1-100 SMG (MP M.34 in Austrian service: 8”/200 mm barrel): 127 grains at 1417 fps (8.25g bullet at 432 m/s) developing 570 ft lbs/770 J
Swiss MKMO and MKPO SMGs (19.65”/500mm and 15.7”/400 mm barrels respectively): 1608 and 1312 fps (490 and 400 m/s). Bullet weight unspecified, but if the usual 127 grains these deliver 773 and 488 ft lbs (1042/656 J) respectively. Personally, I do not trust these figures; the increase in barrel length from 16 to 20” could not by itself result in such a dramatic increase in velocity with this ammunition.
Kiraly/Danuvia 39M and 43M (19.65”/500 mm and 16.7”/424 mm barrels respectively):
Smith/Smith quote 1475 and 1450 fps (450/442 m/s) bullet weight unspecified. If 127 grains, these result in 617/596 ft lbs (832/803 J)
Thompson’s article already mentioned refers to a 156 grain bullet at 1480 fps from the 17.8 inch barrel (that’s 10.1 g at 450 m/s). There was also an AP loading firing a 139 grain at 1645 fps (9.0 g at 500 m/s). These generate 763 ft lbs and 840 ft lbs (1028 and 1132 J) respectively, far more than other figures quoted except for the suspect MKMO one. If the data on these two loadings are correct, the chamber pressures must have been exceptionally high, which I doubt would have been safe in pistols and possibly not in simple blowback SMGs either. I think that would justify them being described as “special loadings”.