Fellas, I feel like I've gotten as deep (in both the positive and negative senses of the word) into the gas piston vs. direct impingement argument as I possibly can however I'm still not settled on which mechanism would be best all around. If I was willing to part with 7K on one rifle right now it would be the HK 416 which uses the gas piston mechanism. However thats about 5K more than I'm willing to part with at the moment. I have carefully considered the SIG 556 which also uses the gas piston design but the strange thing with the SIG 556 is that although it is a gas piston design it also has adjustable valves which allows the operator to open the gas ports more in the event that powder fouling "restricts operation." I have always thought that the true gas piston designs are immune to powder fouling because they basically eject the gases, particulates and powders away from the action and not towards the action as most direct impingement designs ultimately do. I guess if I had to have a summary statement it would be that the typical direct impingement design of most AR15's and AR10's works well when lubed up liberally, and the typical gas piston design of most AK 47's and AK 74's works well regardless of conditions. Other than that one generally accepted guideline I have heard completely convincing arguments both ways about accuracy, reliability, simplicity and weight. After all the independent reading I've done I'd like to learn the wisdom of mud on this topic. So, y'all have any new thoughts on this old debate? Thanks.