I picked up an old police trade in S&W a couple years ago at had been converted to double action only (DAO) for police use. This was a "lawyer" modification police departments did to prevent accidental shootings. The Model 15 is a medium sized K frame and was a common police revolver up until he polymer guns took over, some still remain in service. This particular revolver was made in 1968 and was a police trade in. Meaning that a police department was offered to trade their wheel guns in to upgrade to a more modern pistol, probably M&P 40 cal or 9 mms.
I wanted to convert this "back" to DA/SA for something to do. Some argue that other than target shooting you'll rarely use single action, which may be true but I wanted to have the option.
I ordered a hammer from Numrich who warned me it may require a gunsmith to fit this, in my case it did not but you might not get as lucky.
Here are the hammers the one on the left is the "old" DAO hammer the one on the right is the SA/DA. The hammers are new old stock.
First, of course, open the side plate. I put a little masking tape on my screw driver to protect the screw head. Do not pry the plate off, I was able to just turn the revolver sideways and tap it with my hand and the plate fell free.
At this point I stopped and drew a little picture of what I saw inside and took the opportunity to clean the 40 years worth of gunk built up inside.
I only removed the minimum amount of parts I could to get the hammer free which were the mainspring and the hammer block. Then he hammer just lifted out.
Then I dropped in the new hammer with the SA notch. The easiest way to do this was to pull the trigger all the way back then it slides right in. I pulled the trigger a time or two until it lined up right. I had to push the hammer forward after pulling the trigger since there are no springs .
To put the spring in I unscrewed the screw on the front of the grip. It seemed to work best to put the bottom on the spring in the bottom of the grip attach it to the hammer then tighten the screw.
Putting the plate back on is a bit of a challenge. I struggled to line up the "hammer block" after first managing to put the plate on without the hammer block I finally got it done by holding the plate flat with the hammer block sitting in its grove. then I manipulated the frame until it snapped in.
Then it was simply a matter of putting the screws back in and function testing it.
I've had this revolver for about three years now since I converted it to DA/SA. Years later I'm glad I did. In PA we can't hunt with semiautomatics, while I don't hunt with the K Frame, I have taken it with me for the past few rifle seasons. It's a great shooter, the trigger is very smooth and the heavy steel frame combined with 38 special makes recoil almost unnoticeable. I will sometimes carry it in a Raven Concealment Phantom.
If you get a chance to pick one of these old wheel guns up at a decent price you won't be disappointed.