The Sig 556 the hat I had cycled and fired everything I ran though it. Granted that was a 5.56 Nato... I sold that rifle because it never "did" anything for me. Would you say your ammo problems are because of light primer strikes?
From what everyone is saying, and what I am seeing, it seems Sig quality is going way down hill. How much was that 556R? 1200-1500? For that much money for a gun, there should be ZERO excuses why you had to go though three rifles to get one that was in "decent" condition, and you STILL have problems with it.