Originally Posted by
farscott
Here is the complete list of S&W M27 engineering changes.
27-1 (1960) Change extractor rod, right hand to left hand thread.
27-2 (1961) Cylinder stop changed, eliminate trigger guard screw.
1967 6 1/2" barrel discontinued
1968 Delete diamond grip
1969 Change to N serial prefix
1975 Target hammer, target trigger patridge front sight on 6" and 8 3/8" barrels, introduced with Goncalo Alves target stocks and case
1979 3 1/2" and 5" barrels discontinued, 4" introduced with red ramp and white outline rear sight
1980 Target stocks standard.
27-3 (1982) Eliminate cylinder counterbore and pinned barrel.
1986 Discontinue nickel finish
27-4 (1988) New yoke retention system.
27-5 (1990) Longer stop notch in cylinder.
1992 Discontinue 4" and 8 3/8" barrels.
27-6 (1993) Hogue grips, drill and tap frame, change rear sight leaf, change extractor.
1994 Model 27 discontinued.
27-7 (2000) Performance Center version built on new N frame with floating firing pin and extended frame lug.
So the 27-1 indicates the change to left-hand thread on the ejector rod to stop it from unscrewing under recoil and tying up the gun. The 27-1 variant was made for only a year and is very collectible. The "overstamped" may indicate a forgery or that S&W did the 27-1 upgrade before shipping. As a more common 27-2 cylinder assembly could have been fitted, it is very hard to determine if a 27-1 is original without paying for a "historical research" letter from S&W.