I have this model 15-3 that was a police duty pistol. As you all know, for many police agencies, they would request SW not install a SA sear on the hammer SA sear surface, or they would grind it off.

My 15-3’s hammer sear surface appears to never to have had a SA sear cut into it. I have cut a groove with a precision file and a fire hardened screw driver tip to form my SA sear, but so far no luck on being able to file down the surface to create the SA sear, the case hardening is too strong for my file set.

What kind of files do I need to to file down one side of the sear surface to create the notch for my sear?

Welcome to the forum!

I would strongly suggest that you simply buy a new hammer. There are many different sources on the internet.

If you do succeed in cutting through the case hardening on your existing hammer you will end up with a hardened surface (trigger) mating with a non-hardened surface (hammer) and that won't last very long before it wears enough to become unsafe. That's not to mention the geometry and alignment issues that will pop up.

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SWCA #3942 / SWHF #988

I use diamond chip files and they will cut hardened steel.They aren't very expensive. (Ebay) I just "saved" a 629 that had push off by taking a few thousandths off the sear to make the step deeper. It now breaks clean at 2.5lbs and I "saved" the original target chrome flash hammer. It's not rocket science BUT you have to do it with great care!

Attached Images

IMG_9271.jpg (80.8 KB, 15 views)

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My Daddy was a pistol..

So, I can just drop dbl action sear onto the new hammer without fitting and I would get DA/SA functionality back?

Diamond files are the only way to file that. It's very difficult to get that job right with a file. The S/A notch is only .007 deep and you have to get it exactly 90 degrees to the sides.

The best way to do it is to use a small diameter (1/8") solid carbide end mill in a milling machine. Then you have precision control over the depth and squareness of the cut. Sadly, most people don't have a mill or access to one.

The Easy Button is to get another hammer, as suggested above.

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protocalldesign.com

Get a hammer that has both single and double action sear already on it (almost all of them do). There is a good chance it will be a drop in part without fitting, but not a 100% chance. Sometimes the original D/A sear will be needed, but not too often.

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protocalldesign.com

If you transfer your DA sear to a new hammer, it will likely work properly. If it does not, then a new DA sear will need to be fitted.

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S&W factory revolver armorer

What kind of hammer? I’m looking on eBay and there are different inch measurements for k frame hammers, some are .400” and some are .375”, for a model 15-3 .38 special, which hammer should I get?

Those numbers are the width of the hammer spur for cocking single action. The rest of the hammer is the same.

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protocalldesign.com

Jack First Gun Parts is one of the very best sources of S&W hammers.
Most will be in like new condition.
Buying from sources like eBay runs some chance of getting a defective or worn part.

Smith & Wesson old model K frame 1957-1988 >> Jack First Inc.