Warthog: Actually, they are all recoil operated I believe. There aer two types: (1) Direct blowback pistols cycle the action through the direct force of the detonating cartrdige against the slide - that energy cycles the slide back to recock the hammer mechanism, extract and eject the empty cartridge and the recoil spring then cycles the slide forward to chamber another cartridge. This type of action is used for the smaller cartridges because when you get to 9mm levels the recoil is pretty violent.
Early on in pre-war Germany, Walther developed a direct blowback pistol in 9mm that looked like a oversized PP, but they did not produce it. The Spanish produced two pistols in 9mm calibers in direct blowback, the Astra Models 400 and 600. The 400 was chambered in 9mm. The 600 was chambered in 9mm Largo. The pistol were produced with a very heavy recoil spring as part of their design to help reuce the recoil of the direct blowback design in those calibers.
(2) Delayed blowback or delayed recoil. In these designs the barrel is not fixed into the frame as it is with many of the smaller calibers, but 'hinged' (with a link and a pin) I guess you could call it and moves rearward a bit during the recoil and cycling process. As best as I can relate, when the centerfire goes off, like the 1911, before the slide begins its rearward travel, the barrel is dropped out of battery (lockup with the slide) by recoil and this 'delays' the speed of the slide travel to make recoil manageable (I think I think that's how it works....) and then the recoil spring pushes the slide forward through the cycling process. Most all of the military sized pistols I know of use the delayed blowback system, 9mms, 45s, etc.
I think I'm on track with this. HTH. Mikey.
