The rest of the story: I had a M-617-1 with the round extractor, guide pins and all but the cylinders I ordered from Numrich were both later and non compatible (was originally going to have a .22LR reamed and then the M-648 cylinder) so I was forced to find another M-617 also a dash one but with the more square extractor and no guide pine under it. This was fitted and timed to the newer revolver for the final result. I'm not close to knowing what change the DASH 1 indicated but I had two dash ones and the cylinder extractors were different on each.

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Sam
S&WHF 333 S&WCA 2198