I've been trying to get a couple of old K frames up and running again. One is a pretty rough Victory with a broken mainspring, the other a M1905 M&P 4th change that came with a replacement (flat) mainspring. This replacement spring works the revolver in SA but gives an extremely heavy and rough DA pull. Strain screw appears proper length and is tightened.
With the M1905 I've tried a couple of mainsprings from Numrich, both work in SA but binds in DA. From Kuhnhausen's shop manual, mainsprings in older "long action" K frames with curved hammer stirrups used a curved mainspring. Later "short action"post war K frames(1950's maybe if I recall) used the flat mainspring that everyone seems to carry as a replacement, sold as suitable for all K frames. Have you guys had success using the flat mainspring with the early long throw K frames? If so I'm wrong (not the first time) or misreading Kuhnhausen. Any help would be appreciated. I've been puzzling over this for a while and haven't been able to find any helpful references on the web. Hope that ramble made sense, I've enjoyed this forum for a while.

[I] am a novice , It is strange that it would bind in double action as the hammer does not move as far back as it does in single action . Some of my K 22'S have a main spring with a "S" shape to them not a straight main spring.Experts will be along to help you out soon.