I recently had a Windham heavy barrel rifle transferred through my gun shop. The salesman who was completing the paperwork told me that I should only shoot .223 out of my rifle, not 5.56 NATO. The reasoning he gave was that Windham has a history of marketing their barrels 5.56 when their chamber dimensions are closer to .223. He pointed out that the barrel is only marked “5.56” and omits the “NATO” designation (which was present on the AR’s the store had in stock, and sure enough was present on my non-Windham rifles). He said that this was to remain ambiguous. Of course, he didn’t have a gauge of any kind to back up the claims.
If what he said has any truth to it, I might be in trouble. All I shoot is 5.56 XM193, and I still have a box or two of XM855 left from when that was my main choice. Also, this isn’t my first Windham rifle, so I may have more than one gun that is going towards having issues from over pressure. I did “research” (forum browsing) into the issue and all I could find was the occasional offhand comment about the issue. Does anyone have the truth of what Windham chambers their “5.56” rifles for?
TL;DR: there’s rumors that Windham Weaponry AR’s can only shoot .223, but I can’t find any concrete proof.