Read this elsewhere (TheFiringLine) and thiis is not my gun and I've never handled it yet alone seen it.
FROM THE SELLER.....MORE SPECIFIC INFORMATION: The hammer cocks no problem and the trigger releases the hammer but there is resistance against the trigger and the firing pin doesn't make contact with the cartridge primer. Double action everything cycles properly.
I know Enfields and Webley have an action that is similar to the Colt Python.
Yeah it could be gummed up inside or need lubing, but 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?
Timing comes to mind. I wonder if the rebound lever is dropping too fast, causing the trigger to rebound too soon and the hammer returning to its position of rest before it can go fully forward to engage the primer? I also wonder if the stirrup has been fiddled with. Normally no one works on that but when you study the video, you can see how it pulls back the hammer from being fully forward. The stirrup acts on the mainspring which is influnced by the rebound lever.
I wish I could see and examine the actual revolver in question.
I agree, once you can see sometimes things are obvious. Peter Laidler worked on these and was not altogether adoring in his comments, wonder what he would make of it?
By the way, the revolver you speak of is actually a Webley Mk5? Is that the thread you are looking at? I agree with the statement that "I wouldn't buy a revolver that I knew didn't work"...