I picked this up years ago, it's an early 80s production .38 Special Service Six that was converted to DAO by filing the SA notch off. I'm guessing it was a Security company gun that didn't want their people cocking hammers. I've seen this before on older S&W's, it allows standard thumb break holsters to be used and it was probably cheaper to just buy standard .38 Sixes , take the hammers out and file away then order spurless DAOs from Ruger.
It does it's job, I ran myself through the standard 48 round 3-15 yard Qual Course we used to do on Qual Day with our S&W 65's. It includes 6 from holster retention, and 6 each strong and weak hand. 6 standing then 6 kneeling at 15 yards was always kind of "retro" to me, the Qual Course we used probably dated back to the 1960s
I haven't fired a Six in a few years, and the action is nice on this one. I love guns like this that were used like they were supposed to be used, as working service revolvers by working people. No frills , no "bling" just a .38 that saw a lot of shifts in the holster