I believe Adams was one of the first, if not the first to make a piston AR. Heard good things about LMT & POF pistons too. No personal experience other than my AR180, but that's a totally different animal.
Reading the link now ..... I am issued a Hk 416 Piston Gun and it runs flawless . Wonder what the issues are (reading) ...not looking for a conversion kit. I want a built upper. (Reading) .....:o)
Back in a few ...