Picked up a top break, assume it's 38 S&W, with "reissue" on the barrel with patent dates. The hammer does not lock back in single action but if you pull the trigger, it locks up great. Any help appreciated.
Your revolver is a .38 S&W DA Third Model. The Third Model
was manufactured from 1884 to 1895 (serial number range:
119000 to 322700).
The S&W .38 and .32 DA's lock work used two sears. One
single action sear and one double action sear. I suspect your
single action sear and/or the sear notch on the hammer is
damaged. It is possible to repair these but parts are not cheep.
Jack First Gun Parts lists sears for these on their website: