I would never presume to argue with J.J. He does all of my double rifle work and is damned good. I'm just as confused as Mick is though.

The .375 Flanged Magnum has a head diameter of .517" and the Belted Rimless is .532" (at the belt). They're not even the same case length. The Flanged Magnum is 2.940" and the Belted Rimless is 2.850". Simply enlarging the rim seat to .572" to accomodate the Flanged rim would not deal with the length problem and would leave the first .220" of the Flanged Magnum case unsupported in the chamber (the distance from the breech face to the front edge of the belt of the rimless). The Flanged Magnum reamer won't clean up the Belted Rimless chamber. Bonanza, are you sure that you understood J.J. correctly?

As to the question concerning reliability of extraction with rimless chambered doubles, I don't know if Westley Richards invented the current system or not, but they certainly pioneered building doubles in rimless calibers. They built quite a few and there doesn't seem to be a collection of stories from the old days about failures. I've always heard that their system was reliable.

I avoid rimless chambered doubles and as a result have only shot two. Oddly enough, both were Westley Richards, a Gold Name boxlock in 9.3X62 and a droplock in .318 WR. With the 9.3, failures to extract approached 50% with Norma ammo due to the extractor pawl slipping over the rim. RWS was much better, but we still got failures to extract every trip to the range. This rifle had been gone over in London by Paul Roberts specifically for this problem the year before. Only had one range session with the .318 and only late production original Kynoch was fired. As I recall, there were one or two failures to extract and a similar number of failures to eject.
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