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With all of those being gas guns you are not going to get good results, even with the adjustable gas block you will likely run into some issues... What is your goal with shooting subs? Also what cans are you using on the different rifles?
What do you mean by "still operational"? If you mean to find subsonic ammo that cycles those rifles, forget it, it doesn't exist and isn't going to. Your barrel twist rates are too slow for the heavy bullets, and the cartridges are not good subsonic performers for cycling an AR action.
Maybe I missed it but not a single person in that thread claimed they could make a sub sonic cycle. They even talked about just turning the gas off and running it like a bolt.
I understand all that, these weren't built for sub-sonic...but I have read of some doing some work on it...there seems to be some disagreement that the winged unicorn exists. Came across this on 68forums of a few loads that actually cycle the action. http://68forums.com/forums/showthread.php?5642-I-have-a-subsonic-load-nearly-perfected