It is not only the West that has developed small caliber, high-velocity pistol-compatible personal defense weapon ammunition; in the early 1990s, the People’s Republic of China also developed such a round. Called the 5.8x21mm DAP-92, it fires an 0.229″ caliber dual steel/lead cored bullet at a nominal 1,738 ft/s from the QCW-05 (Type 05) SMG, or 1,574 ft/s from the QSZ-92 handgun. It is shorter and less powerful than either the 5.7x28mm FN or the 4.6x30mm HK, making it a more suitable round for use in handguns than its Western counterparts.
We can see how it compares to some of its stablemates in the charts below:
Initially I was pretty lukewarm about the 5.8x21mm because of its relatively low muzzle velocity compared to its stablemates, but I now think I understand the rationale behind its design. The lower muzzle velocity allows the use of a higher weight and consequently higher BC projectile without incurring high penalties with regards to recoil and flash, and this higher BC bullet retains energy much better, meaning that although the 5.8x21mm starts with the lowest energy of all rounds on the chart, it ends with the highest amount of energy of all the high velocity rounds – though still significantly below the 9mm.
However, I think this strategy likely comes with the penalty of a lower maximum range where the round will penetrate certain kinds of armor. There isn’t a direct equivalence with which I can prove this, but the 5.8mm DAP-92 is listed as penetrating a 1.3mm helmet out to 100m, whereas the 5.7mm SS190 is rated to penetrate a CRISAT vest (a 1.5mm titanium plate backed by 20 layers of kevlar) at 200m from a P90.
By weight, the 5.8x21mm ranks very highly, being listed at a mere 6 grams per round in official Chinese documents. That is half a gram less than even the diminutive 5.7×28!