BudsGunShop.com - direct impingement or other is BEST

John, a very good operational comparison is here Sir : youtube.com/watch?v=feuWaWIAf5E

John, DI is the most common. Direct impingement is a type of gas operation for a firearm that directs gas from a fired cartridge directly into the bolt carrier or slide assembly to cycle the action. Direct impingement rifles are generally more accurate than their piston counterparts. Gas piston. While heavier than direct impingement models, gas piston AR 15 rifles run considerably cooler and considerably cleaner due to an absence of gas rerouted back into the rifle. So, the main difference in the Piston system is that instead of a gas tube, it has an actual piston drive rod. When the bullet is fired, the gas travels down the barrel to the gas block. Instead of traveling back to the receiver through a tube, the gas pushes a piston system and then escapes out of the gas block. See this link:-westernsport.com/difference-between-di-piston-ar/