Grooves for dust covers were machined in frames up to around S/N A300000. They were not popular as they served no real purpose and tended to wear off the finish on the slides. I bought three guns that had them but quickly removed them as soon as they arrived. They could be ordered as a separate item but didn't routinely ship with a gun unless requested. Interesting that S&W never obtained a patent for them.Early one ..... first year?
Guess not marked Model 39. I thought the dust covers were only on pre-39s?