Gentlemen, welcome to you both.
Harl: The 17 looks like 1959; the 28 1979-80; the 57 from somewhere in the 1982-84 range.
Dawg, your 27 looks like 1976; the 29 is roughly the same age, but maybe a little earlier -- say 1975.
Credit for these dates goes to the serial number table at the end of the Standard Catalog of Smith & Wesson (Supica/Nahas).
Hint: we like pictures here.
David W.