My first AR was in x39. It was a bit of a Frankenstein but mostly PSA with a Tactical Ambush BCG. it was built several years ago and I got it through an estate sale. The only real problem I had with it was the M4 feed ramps were designed for a .223 so I had to open them up to .312 but I think most rifle manufacturers have learned that lesson. I’ve heard that some mags are better than others but I’ve heard that about every caliber out there. Just buy good mags and test each one. Other than that I have no problems with my commie AR. Runs like a top. A very mean, bad ass top 
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