Pistons short-stroke more because the force from the gas must overcome the weight of not only the bolt-carrier, but also the piston rod. It's simple physics: more force is required because a quantifiable amount is lost to overcoming the inertia of the piston rod. With a DI gun, the only mass that needs to be moved is the bolt carrier. This means a round that is just barely powerful enough to run in a DI system has a very high chance of short-stroking in a piston gun. It also results in higher failure to lock back after the last round is fired.
The act of piston rod hitting the carrier will jolt the gun, literally. Maybe you don't notice it, but it's happening nonetheless. It's the same reason that carrier-tilt happens. Instead of a smoother, more gradual gas expansion inside the gas key on a DI gun, the piston simply slams back on the carrier and the energy is directly transferred as a physical force into the upper receiver and into the rifle. The DI guns don't have this because their isn't a direct physical transfer of energy (since gas is essentially a fluid and will flow to the path of least resistance) and the only felt recoil is a result of the carrier connecting with the buffer.
It's like a rope: you can pull on it gradually, or you can yank on it at full force. The piston guns will always have a "yanking" effect to them. DI guns won't (speaking relatively about the same gun firing the same round).



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