Last year, I finally bought an AR and opened up a huge can of worms. Now I constantly obsess over getting new calibers in the AR platform. I have shot and owned several semi-autos but nothing larger than a 7.62x39. Anyhow, I just wanted to hear opinions from anyone who has shot or owned an AR in 6.8mm or 7.62x39 cals. Are they worth the investment or should I be saving up my pennies for an Ar-10 ?