Received my Sig 556 back today. The forensic engineers examined the barrel and found that a "squib" round was the culprit 35cm from the breech that expanded the barrel in excess of 4.7mm at the muzzle flange.
They also said these results were similar to "tests" conducted by the R & D dept. Very professional, and it took one month.
Mr. Ray Carter in customer service, was very helpful, although he did not return my voicemails, but did answer personally two days later.
SO, they charged me a time and trouble fee (not warranty), $100.00. and $14.00 shipping. and installed a brand new barrel.

For a $1200.00+ rifle, paying full retail for a replacement barrel, I'm sure would be more than a C-note. Alas, I got her back!!
Just one of those things, I was denial about a squib, since I shoot new, name brand ammo (except Wolf). But its back and I am thankful.
Overall I'm pleased, they explained in painstaking detail what happened, and cut me a big break to replace the barrel.
I saved all my cans for this weekend.
