Fishtail top lever right hammer.

[B. Dudley]

The hammer that I photographed was notched so that the gun would open with hammer UN COCKED.
It was a 1 frame hammer gun with fishtail lever.
The fishtail allowed opening when cocked and the notch allowed opening when uncocked.

[edgarspencer]

Originally Posted by Brian Dudley

The fishtail allowed opening when cocked and the notch allowed opening when uncocked.

I would think any hammer gun could be opened, un-cocked, without the notch.

Here's Gary's Grade 3 hammer gun:

[C.O.B.]

I wonder if Parker notched the hammer on the request of the original purchaser. I have never seen another example of a notched hammer.

This could have been done after the fact also by the owner. Just another possibility.