Most of the Ruger Mag cylinders are unfluted. A very few for the three screws are fluted and have recessed heads for the cartridges.
The model RSSM, Ruger Single-Six Magnum, was produced in the '59-'62 era. Approximately 42,000 were shipped with fluted .22 mag. cylinders.
The Single-Six Convertibles were introduced in mid '60. Tens of thousands of these guns were produced.
So, perhaps "most" are unfluted but there are a lot out there that aren't.

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