[4V50 Gary]

Like other DA/SA revolvers, the Webley's hammer has a single action notch that engages the trigger tail. In the SA mode, the trigger tail is engaged against the hammer's single action notch. When pressure is applied to the trigger, the tail rotates forward and disengaages the hammer's single action notch. Pressure from the mainspring via the stirrup should cause the hammer to rotate forward. Unlike the Python there is no hammer block or (like Ruger) transfer bar that can break and impede the hammer's rotation.

Clearly something is intercepting the hammer's rotation from completing its forward movement. I wonder if the hammer tail is deformed such that it catches the DA sear OR if the DA sear is deformed such that it strikes the hammer tail and stops the hammer from rotating fully forward? Or it could be just in need of a detailed cleaning. Hard for me to say w/out examining it.