I read an article in the Guns and Ammo "Book of the AR-15" recently and it gave a good review after a real torture test through mud, water and sand. They even would dunk the hot barrel in water every so often. It seemed top get good groups and they could not get it to fail. I think they said the test rifle is up to 20,000 to 30,000 rounds now with no fails. To Quote: "The SIG516 is said to be the fulfilled potential of every AR. Proven accurate, durable and reliable, it still retains the AR's modular concept and accepts rail-mounted accesories...."
Seems like it would be real work horse and I would love to try one out sometime.