One company bought a bunch (200+) from me and then handed the nut to a local machine shop, copied it exactly, and then continued to re-sell it as having been manufactured by me. When I found out I had a not-so-nice conversation with their management who's attitude was "who cares, there's nothing protectable about it". Which was true except for the part that they were selling it as having been made by me when it wasn't and used our name to sell it.
It wasn't OMR.
We had several barrels in here recently that were made elsewhere, two of them were very well known name companies. They didn't pass a set of gauges correctly, in fact one of them wouldn't even start a GO ring for 1-1/16x20 Class 3 but it did screw onto a TL3 and an Origin fine.
I use standard gauges for every barrel, nut, brake, thread protector that I make. I don't thread to fit anything. Sometimes this means that parts from other places don't fit our parts when that other place is using a mating part as a gauge or not gauging in production. Sometimes it means that a part slipped through production checks. It happens to everyone, once in a while it happens here too. I spent a small fortune on gauges for every single item that I make now. But my phone rings a whole lot less for stuff that doesn't fit properly.
You're not the first person to have an issue putting a barrel nut on a barrel and I'm sure you won't be the last. I just won't make barrel nuts on a Class 1 fit to make sure they fit everything out there.
