S&W 66, can't tell the "dash" number by the photo but it is what is now referred to by S&W collectors as "pre-lock".
The "lock" is the unsightly action lock, located above the reshaped cylinder releases on S&Ws produced after their landmark cave-in to Clinton, agreeing to equip all new handguns with action locks.
The lock is reputed to seize the action on the D/A revolvers all by itself. The first people reporting it were deemed too stupid to operate a revolver but more and more incident accounts rolled into gunsmiths, forums, and magazines.
The difference in price between pre-lock and lock on the same model can be $300-$500 and more, depending on rarity of the model.