Uncommon?
Not sure I’d label this 4th model uncommon. Very scarce is what I’d call them. Those few that I’ve seen are normally found in the condition of the OP’s gun. Very desirable among Merwin collectors.
*** Also, you have to be very careful with these. There are Foreign copies out there that are very often mistaken as authentic Merwin & Hulberts.
What does the barrel address say. Word for word?
Also, it’s a 44-40 Winchester caliber. You can see the 73 on the frame. See photo.
The late hammer is typical of post 1884 production. So this is a late one and low production.
I’m kinda suspicious about it though. That 73 stamp looks odd.
Murph