Perhaps. But it was brought up that the Mini-14 is different (from the AR) because it has a piston. This ignores the fact the AR has a piston.

The AR does NOT use a direct impingment system. The AR uses an expansion chamber inside the carrier. The direct impingement system does not. In the direct impingement system, the gas flows from the gas tube directly a small piston fixed externally to the carrier. This pushes the carrier rearward to unlock the bolt.

In the AR gas system, the gas flows through the gas tube to the gas key. From the gas key, it flows into what Stoner calls an expansion chamber. Inside the expansion chamber (cylinder) is the piston, the tail of the bolt. When the gas in the expansion chamber reaches operating pressure, the carrier is pushed to the rear. The piston (bolt) remains fixed in place until it is unlocked then pulled back with the carrier.

There are exhaust ports in the right side of the AR carrier. You can see them if you look into the ejection port. When the carrier moves enough, the exhaust ports are open and the gas vents through them.

If you look up the original patent covering the gas system, Eugene Stoner states it is not a direct impingement system because his system uses an expansion chamber. The US Patent Office agreed when they approved the patent.

If you check Colt's literature describing their AR, you will see they describe the gas system as a "direct gas" system, not direct impingement.

It is not pointless to compare the AR gas system to the Ljungman because the Ljungman is the prime example of a direct impingement system. If you study the Ljungman, you can see the difference betwen it's DI system and the direct gas system of the AR.

The AR is a piston system. The difference between it and the Mini-14 or the AK is that the piston in the AR is located in the carrier inside the receiver, not the gas block.

If we were just splitting hairs, I would point out that the AK is more like a direct impingement system than the AR. The AK has a piston fixed externally to the carrier, just like the Ljungman. The only difference is, the AK piston is longer and its gas tube shorter.