I have built 12-15 AR's in the past with very few problems. I had been buying most of my parts from surplus ammo and arms. I switch to Palmetto arms for these last 3 builds 2, 6mm ARC's. The ARC's worked fine. I used a 20" Nato 5.56 that came from midway AR-Stoner 1-7. I put on a rifle-length...