Big Larry...5-screw and 4-screw revolvers were shipped concurrently through the first six months or so of 1957. After that, most were 4-screw revolvers with a few 5-screws being shipped (some models that were slow movers like the 1950 Target 45 and 38/44 Outdoorsman continued to be shipped with a 5-screw frame until around 1960). The earliest 4-screws were shipped in February/March 1957 and had a serial number in the S167400 range.

Bill