I tried that AR Stoner and had to return it. Both the bolt and barrel had issues. Let's address the bolt first. For some reason the bolt would not let the firing pin go in far enough to give a decent strike on the primer. I changed out the bolt to another I had, and no issues. BTW, "matching" bolt it is not. The bolt was brand new, no wear marks off the black, and we KNOW that cannot happen if they matched the bolt to barrle in headspace. There would have been an indication that the marks from the barrel lugs met the bolt during that process. As is, it was pristine...kind of like an magic bullet from Dallas.
The barrel shot a pretty nice group, even for new. I did recover a bullet and it had mushroomed well and the rifling groves were very clean, neatly cut and free from evidence of slippage. I have seen fired bullets that had sliped in the path down the barrel and leave a telltale mark on the bullet. The chamber was what was the issue. During the chamber reaming it had incurred a grove near the start of the shoulder. That small grove didn't and wouldn't have affected single use of the brass, such as someone who just buys new bullets and fires and forgets them. But, to a reloader, that groove would spell premature doom to the brass from repeated resizing and re-grooving. If I would have had a 6.8 SPC II reamer, I might have been able to removed enough of the material in the chamber to have eliminated it, since chamber dimensions do have certain + tolerance values. But I sent it back, got full refund back into my account (to MidwayUSA's credit for good customer support), as well as initial shipping costs. I waited to get another barrel, figuing it was a fluke. Barrel was supposed to be back in stock on 11/15/2010 so on 11/15/2010 I checked the sight again, and now it showed new arrival date of 12/01/2010. Next day it changed again to 12/31/2010, so I started looking elsewhere, which led me to Harrison, AKA Constructor, of AR Performance with his barrel. His came in a timely fashion, was reasonably priced, had great specs, including the 5R rifling, and shoots under 1/2" group with the right load.. actually one group of 3 is covered by a penny.
I contacted E.R. Shaw by phone, twice, and they are insistant that they do not make a 1:12 5R barrel at all. I never did find out who the actual company is that makes these barrels, but those specs are rather unusual in the industry of barrel making for the 6.8 X 43.