SW model 439 SA/DA issues

[Green Frog]

What ammo are you using! I’m guessing that may be your problem. Otherwise, I’d look into a replacement hammer. The gun has been out of production for a long time but used and NOS parts are readily available.
I have a Model 639 (same gun only stainless) and I’ve played with it like an Erector Set, changing parts with carefree abandon, and have never had this kind of problem.
Froggie

 

[Doug M.]

I have to agree with the recommendation to send it to BMCM. I have seen his work on 3rd generation S&Ws posted, and it is always professional. I have had him do a couple things for me, and likewise. You are likely to have a reasonably quick, fair priced assessment and repair, and thus put an end to your frustration.