I'm very very green when it comes to ARs, M16s, AKs, ACRs, etc. So bear with me. I want to build an AR15 sometime in the beginning of next year (when finances allow), but it's lead to a very interesting debate I didn't know existed, why would you choose gas piston over a direct impingement system? I was reading about the Bushmaster ACR (and watching the future weapons episode) and noticed they went with a piston system, and then boasted that their rifle was half a pound lighter than it's M16 counterpart. If weight was such an issue wouldn't you go with DI instead? What advantage does a piston system have over DI? many of the people I know have said it's largely a solution to a problem that doesn't exist. Both systems require cleaning and regular maintenance, it's not like the piston system never gets fouled up. If you took care of your rifle like you're supposed to, is there ANY advantage? For people like me who will likely never see combat, nor spend weeks at a time firing off shots without cleaning my rifle, is there any good reason to go with a piston system? I'm just trying to wrap my head around why magpul would design the assault rifle of the future and then slap a piston on it. What am I not understanding?