OM vs NM .22 cyl body lengths:
“Early” OLD Models Lightweights and pre lightweights measure 1.390” +/- in the body length,
“mid” old models beginning about 1960 are 1.405” +/-,
"late" old models and those in new model guns are 1.410" +/-.
The change from old design to new design vs OM/NM guns:
Did Ruger use up blued Old Model, old style cyls by shipping with New Model blue guns? Some blue cyls were.
They weren't all left over old model cyls in blue: they were continued to be made in the old style design and began being made in stainless (there were no OM stainless guns or cylinders). In other words, the change in cyl design had nothing to do with the New Model change, it wasn't simultaneously introduced and not until after introduction of the New Model SA design!
You can call them "new model or new style cylinders" but they were not part of the "New Model line" of single action transfer bar safety gun re-design. They were a later and separate production design change.
All of the Old Model Super SS and Single-Six had fluted 22 and 22 Mag cylinders. The non-fluted Mag cylinders started in 1975, after the New Models were introduced in 1973 for the Blue guns and in 1976-1977 for the Stainless Steel guns. The elimination of the firing pin groove in the 22 LR cylinder does not coincide with the introduction of the non fluted Mag cylinders but there are transition guns with both old type cylinders or an old type LR cyl. with the new non-fluted type Mag cylinder. The blue guns switched to the new type cylinders around 64-15000 to 64-17xxx c. 1975 or so before the 1976 Liberty marking and the stainless guns switched about 64-70000 c.1977, after the Liberty marked guns.
