My Mk VI was made around the same time, but suffered the all-too-common indignity of having the cylinder shaved for .45 ACP moonclips.
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I just shoot .45 Autorim brass in it, downloaded significantly. It would be nice to find a spare .455 cylinder/extractor assembly for it, but they seem to be unobtanium and I have no idea how much fitting they would require.
Speaking of missed opportunities, I've seen adverts like this one from a few years before I was born offering ,455 Webley revolvers and automatics for $20.
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