I have used 5 of their uppers 5.56, .223 Wylde, 6.5 Grendel, 450 Bushmaster & 350 Legend. They all, surprisingly, shoot moa or better, the . 223 Wylde shoots . 5 to . 6 consistently. The only problems I've ran into are the 1st gen side charger retaining bolt would come loose (6.5 Gr) which...