Can anyone briefly explain different gun operating mechanisms like DI/short stroke/blowback with 1/2 popular examples?
• DI or Direct Impingement
There is no gas piston or gas cylinder; the gases directly impinges on the bolt face. Extremely simple but inefficient so only two three guns use them. MAS-49 is one example
Interestingly AR-10/15 is not a DI based gun
• Short Stroke
Gas is vented from the barrel to a piston assembly which then cycles the gun. What makes it "short" is the fact that the piston travels less than the distance of the cartridge. All modern assualt rifle are more or less SS; SCAR, Bren, MSBS Grot
• Long Stroke
Same as SS but here the gas piston travels the whole length of the bolt cycling. Almost all machine guns are Long Stroke, so are all AKs.
• Blowback
The only system that's "unlocked" meaning the bolt and barrel are not positively locked and are just together using either spring tension or some delaying mechanism. It's the simplest as it works on action-reaction principle. Gases push the bullet down the barrel and the same gases pushes the case rearward, which cycles the gun. Except for few all SMG are simple blowback; MAC-10, Uzi, Asmi
• Delayed Blowback
Same as blowback but there is some additional mechanism that creates a mechanical disadvantage for the bolt causing it to open slowly; these can be roller/lever/cam/gas/radial delayed blowback. All of H&K's previous generation of guns are roller delayed blowback; MP-5, G3, HK-23E.
• Quasi-DI or DI-SS Hybrid
An ingenious way invented by Eugene Stoner to use half the DI system and the actual bolt as a short stroke piston. AR family of guns are the best known example.
• Short Recoil
Here the bolt and barrel are locked together during the initial phase of firing and they both "recoil" together for a distance less than the cartridge length; after this the barrel stops and the bolt continues. Almost all modern semi-auto pistols use this only; from the very first 1911 to the latest CZ P series pistol.
• Long Recoil
Same as Short Recoil but just like SS Gas Piston the barrel and bolt travel the whole distance of cycling. Kind of obsolete system; Auto-5 is perhaps the best example.
• Interia
Bit difficult to implement so currently only low powered shotguns use it. Here the interia of the Bolt Carrier Group itself is used to operate the gun. Can be very easily confused with a blowback system but it's a locked breech system as opposed to unlocked of blowback.