Interesting or odd - hand fitted thumb-piece

[Protocall_Design]

It looks to me like the only mod to the one in the picture was to try to make clearance to keep it off the frame.

The mod described above, where you shorten the part that goes in the frame is to make the cylinder turn easier. The way it does this is to take compression off the center pin in the cylinder. You can easily check this condition by pulling back on the thumbpiece with the cylinder closed. There should be a small amount of rearward movement of the thumbpiece. If not, then the center pin is under compression, pushing the cylinder forward. It's easy to file some off the back part of the thumbpiece where it goes into the fame to create a clearance. I like to keep the rounded end profile so it looks the same as original, just shorter lengthwise.

Under normal heavy spring circumstances this will go unnoticed. On a quality action job there will be a noticeable difference in trigger pull if this is done or not.

 

[JohnHL]

My guess?

Fitter was given a frame and thumbpiece with excessive clearance.
Fitter made a few more file strokes on the basepad than were needed.
Fitter then filed on underside of thumbpiece to compensate and passed the job along to the platers.

In essence, one dubious action to compensate for a mistake.

Happens all the time in the real world to speed up production.

John