Yah... damnit... i need to keep these threads saved somewhere. I believe the rollmasters have the least problems or better chamfer than the jp's, they explained it and measured it before in other threads and pics, zoom also mentions in the new thread that rollmasters have a lower failure rate. They have always made the double jp and double rollmaster. And about above, the chains may be of lesser quality or it could be breaking due to uneven wear caused by the sprocket being unaligned. Basically the double chain will function as a single roller because it places pressure unevenly.
You could find a local machinist when doing your build and take both the stock sprocket and the new sprocket and have him match it. I thought thats what farns did, or at least someone did... they said their local machinist was very experienced and did it by just looking at them both and later doublechecked the chamfer and was almost dead on, thats what i remember reading. I'm just a ****in librarian without a card catalog! lol