My Dad carried a 6" .357 magnum Colt New Service before the war...... and after through the 60s..... he also had a 4" S&W M&P .38 (1946) and a 2" Colt Detective Special for court and off duty.

I think the 5 and 6 inch service revolver was more the norm through at least the mid-50 with the Model 19's introduction........ with a mix over the next 15 years or so...... think the Highway Patrolman in 6 and 4 inch..... with the 6" seemingly more common.........

I think the move to 4" guns really came about with officers/Depts switching to the 64,65 and 66 in the 70s.