Your S&W revolver push-off condition is caused by a mismatch of hammer sear and trigger sear surfaces.
Commonly, the trigger sear is rounded off or simply not as sharply defined as it needs to be. In extreme cases, it may be rounded by inexpert stoning. Seldom is this caused by wear or dropping damage.
A few strokes with a fine stone is enough to clean up the trigger sear surface.
CAUTION: S&W triggers and hammers are case hardened. Too much stoning, or worse, filing will go through the case into the soft steel, making the gun unsafe.
If you are not experienced at S&W revolver disassembly, you might want to have a qualified gunsmith work on it.
