Warrenb,
I thought of that with my first 7600 and also measured the casings. You are correct in that they did not appear to be to far out of spec, so to speak. I consulted with two gunsmiths and had one check the headspace. One I spoke to referenced the chamber oversizing and possible need to index the barrel. The other, whom I bought the gun from, noted that checking the headspace on a 7600 is a bit tricky and his results were inconclusive. In looking at the rifle (with the mag out) I noted that the bolt does have a slight movement when closed.
The bottom line was that we sent it to Gravel's and they replaced it. The replacement performed similarly. On second shot, the casing (about 1/4" from the head), regardless of whether the first shot was new factory or new brass, had a noticeable "bump" in that area. You could feel the bump where the case had stretched and would fail. Two rifles, with the same problem (maybe from the same batch) I dunno, that was the tale of the tape for me.
And yes, you are right, the barrels are fantastic as they are truly free floating and are good, fast shooters.
