This revolver came from an Internet auction and I really didn’t know what it was until it arrived and I disassembled it. The serial number is 251153 and the Model of 1905, Fourth Change was supposed to start with #241704, about 1915. This one was probably shipped that first year. I bought it mainly for the grips, having never owned a K frame with large (.500”) medallions, round butt grips. They may be pencil marked with the serial number, but extremely faint but perfectly fitted to the frame. It has several other very early features including the lack of a hammer block, a featured added to this model (Neil & Jinks,
S&W, 1857-1945 “added to round butt July 1, 1926”). It also has trigger and hammer chafing bushings and two extractor pins; this model mainly had one pin and no bushings. These early models had a spring and plunger in the yoke that holds the cylinder open, when fully opened. This feature was discontinue some time in the late 1920s.
1905 Round L-
Cylinder Open-

Right Grip- Inside-
I have one other square frame with the yoke detent which hold the cylinder open and I guess is seen on pre-1920’s revolvers, very cool feature!
Yoke plunger & spring- Yoke Detent Close-up-
Depressing yoke plunger-
This spring and plunge is quite commonly missing as it can fly out during disassembly and except for the cylinder not staying open, the revolver will function normally. The photo above show the plunger being depressed for installation with a screw driver but a thumbnail will probably work just fine. I gave the revolver a thorough cleaning inside and out then photographed it for your perusal. It looks to be very little fired but unfortunately has quite a bit of holster wear and a bad scratch on the sideplate!

I recently discovered that some early N-Frame S&W had the hold open feature so I disassembled my 2nd Model .44 Hand Ejector and lo-an-behold it had the hole in the yoke and recess in the frame, but no spring or plunger. Later that afternoon I made and installed the parts.
This .44 was shipped from the factory September 2, 1924, to Shapleigh Hardware Co. St. Louis, MO.

Second 44 Left-
Without and with new plunger and spring.
Yoke Detent hole-44 Plunger-
Miraculously the cylinder stays open!
44 Cylnider open-