PT. PINDAD, the Indonesian government owned firearms and ammunition manufacturer, once made an interesting pistol called the PINDAD PS-01 ‘Serbu’ (Assault) Pistol.
The PS-01 was unique for two reasons. The first being its large frame and long 7.4″ barrel. It weighed in at a hefty 2.64 lbs. Despite being similar in size to gas operated pistols, such as the Desert Eagle, it was a standard blowback operated semi-automatic.
The second reason it was unique was the cartridge it chambered, the 5.56x21mm PINDAD. The 5.56x21mm PINDAD is a cut-down 5.56mm NATO round. Judging from photos of the round, it probably had about the same power as the .40 S&W or 10mm Auto cartridge but, with its small caliber and light rifle bullet, the velocity would have been impressive, as would be the barrel wear and muzzle blast.
The advantages of this cartridge, in combination with a heavy frame, would have been good range, accuracy and armor penetrating capabilities compared to a conventional pistol.
The gun no longer appears to be manufactured, it ever was. It is not hard to see why it was a commercial failure. It lacked the benefits of a submachine gun or rifle while also lacking the compactness of a conventional pistol.
[ Many thanks to Gunhead for emailing me info about the pistol. ]