In starting my research for my next rifle build I'm looking at this new type of system - the gas piston. So far it looks like the gas piston system is a cut above the standard AR15.
When the rifle is fired, the developing gases expand inside of the gas block much like a traditional DI system. The expanding gases push against our short stroke piston which exerts pressure on the operating rod and thus gives momentum to the bolt carrier. Once the piston itself has traveled 3/4", it expels any unused gas from a small vent in the bottom of the piston tube. As the cycle of the action is already in progress, the piston moves to the back of its chamber awaiting the return of the operating rod to push it back into battery.
Here are a couple of animations that show the differences. (you can toggle between the HK for the GP and the AR for the DI by clicking the button in the bottom right corner)
The primary benefit of going Gas Piston is a higher level of reliability by running a cleaner and cooler AR by moving the operation of the rifle from the upper receiver and bolt carrier to the front gas block using a small diameter short stroke piston which does not require constant cleaning or lubrication like a Standard DI (Direct Impingement) AR does in order to ensure functionality.
Also, you can have your AR cleaned in 5 minutes, vs. 30 minutes with a normal AR.
The Bolt Carrier and Charging handle are broken down the same way, and the Gas Piston Tube is located inside the Gas Block and is removed by pressing on the piston tube nut release button, turning the tube and removing it by pulling it out.
Then the tube is broken down very easily by removing the cross pin, removing the nut and taking the piston out of the tube.
As for recoil - with the Standard AR the action is direct blow back into the upper receiver and the recoil is felt more in the upper receiver, closer to your face and shoulder.
The Gas Piston System uses a small diameter piston that only travels about 3/4" and meets the fixed op-rod (which is affixed directly to the Bolt Carrier Group). The Recoil is not as harsh since the action is now occuring in the gas block at the forward part of the rifle, plus the excess gas is blown out of the gas block.
Does anyone have any experience with a gas piston system and what do you think?