Let me start by thanking JohnHL for his advice and suggestions. If this project works out, he deserves significant credit. If it doesn't work out, it's because the guy doing the work his ham fisted.
A few weeks ago, I read a couple of threads about the various DAO 3rd Gen guns. As we know, the 3914DAO has "double strike" capability and was specifically designed that way for the NYPD. At some point, I asked how hard would it be to convert a 3914 to DAO.
JohnHL answered and told me that it was a matter of filing the Single Action notch off of the hammer and getting a firing pin retainer from a later 39/40 TSW, although the safety/decocker could be retained.
I didn't have the courage to modify my 3914NL, plus firing pin retainers are hard to find and expensive.
I also have two 457s, so I decided to take the older one and see if I could pull the modification off.
At Numrich, I found a firing pin retainer for a 4586 for about $22.00. I also ordered new firing pin and main springs.
I bought a pile of used parts on Ebay, which included a hammer and sear. Also included was a main spring cup, more on that later.
When the trigger arrived, I set to work removing the SA notch. Much hand filing was done over a period of days. I avoided the temptation to use a Dremel tool. Whenever my eyes cast longing glances in that direction, I put down the file and took a break.
Once I got the notch removed, I smoothed the area with a Scotch Brite ultrafine (maroon) pad until it was smooth as silk.
Here is a before,
and after
picture. I apologize for the quality of the pictures. I meant to take more, but forgot, and now that everything is back together, I'm NOT taking it apart again.
I then turned my attention to fitting the firing pin retainer. A bit of filing was needed, but the part fit fine.
I reassembled the slide with no problem, then took a few days off from the project.
Friday night I had nothing much to do and decided to "look at" how much was needed to swap the hammer. One thing lead to another and before I knew it, I had the grips off, hammer out, along with the firing pin spacer, ejector, sear, and other parts out.
I've viewed the assembly/disassembly videos on YouTube a number of times and it didn't look too hard. As the man in the video says, the hardest part is keeping all of the parts lined up.
He ain't lyin'.
I lost count of the number of times I had the ejector, firing pin safety, hammer, and sear release lined up with a pin punch through the hole to keep them in place. That wasn't too hard, the hard part was not letting the pin punch fall out while trying to get the disconnector and sear into place. At which point, I'd lose my grasp on pin punch and all of the other parts would fall out.
I finally got those parts in place, and then spent another half hour getting the sear in place and held in by yet another pin punch.
This is where having four hands would have come in handy.
I finally got everything back in place, put the main spring and plunger placed into the Hogue main spring cup and got that in place. Now, to put in the grip pin.
This is where having six hands would come in handy. The Hogue piece came loose, the plunger and spring followed it and they all went into orbit.
At which point, the pin punch fell out and the hammer, sear release, ejector, and firing pin safety fell out. Again.
Sigh.
After finding the new main spring, and assembling that with the other main spring plunger and a spare Hogue piece I happened to have, I started again.
Finally, I got everything in place and put the sear pin and sideplate back on, followed by the grips.
Viola!
I've dry fired this a few times and there are no bad sounds from inside or weird sensations. The trigger action is smooth and it has double strike.
It's supposed to warm up later this week and I'll make an attempt to get to the range to see if and how it shoots.
I've retained the original trigger and sear and will be able to restore the gun to original condition if needed.
I still have to figure out what to do about matching the stainless firing pin retainer to the slide. There are a few ways to do it, but I'm looking for one that won't cost as much as the gun did.
I'm relatively sure that the people who built these guns at the factory had training, techniques, and tools to make it much easier than it was for me. The YouTube videos are helpful, but it takes a lot of dexterity to put the parts of the frame in properly. JohnHL is convinced that it requires people with finger joints that move in directions not normal for humans.
My thought is that there were several young children with small, but strong fingers, involved.
It can't be too hard, because I've been casting and eye towards a LGS that has a very clean 3914 and searching for a firing pin retainer.
OTOH, I have a very nice 3913 ...
A few weeks ago, I read a couple of threads about the various DAO 3rd Gen guns. As we know, the 3914DAO has "double strike" capability and was specifically designed that way for the NYPD. At some point, I asked how hard would it be to convert a 3914 to DAO.
JohnHL answered and told me that it was a matter of filing the Single Action notch off of the hammer and getting a firing pin retainer from a later 39/40 TSW, although the safety/decocker could be retained.
I didn't have the courage to modify my 3914NL, plus firing pin retainers are hard to find and expensive.
I also have two 457s, so I decided to take the older one and see if I could pull the modification off.
At Numrich, I found a firing pin retainer for a 4586 for about $22.00. I also ordered new firing pin and main springs.
I bought a pile of used parts on Ebay, which included a hammer and sear. Also included was a main spring cup, more on that later.
When the trigger arrived, I set to work removing the SA notch. Much hand filing was done over a period of days. I avoided the temptation to use a Dremel tool. Whenever my eyes cast longing glances in that direction, I put down the file and took a break.
Once I got the notch removed, I smoothed the area with a Scotch Brite ultrafine (maroon) pad until it was smooth as silk.
Here is a before,

and after

picture. I apologize for the quality of the pictures. I meant to take more, but forgot, and now that everything is back together, I'm NOT taking it apart again.

I then turned my attention to fitting the firing pin retainer. A bit of filing was needed, but the part fit fine.
I reassembled the slide with no problem, then took a few days off from the project.
Friday night I had nothing much to do and decided to "look at" how much was needed to swap the hammer. One thing lead to another and before I knew it, I had the grips off, hammer out, along with the firing pin spacer, ejector, sear, and other parts out.
I've viewed the assembly/disassembly videos on YouTube a number of times and it didn't look too hard. As the man in the video says, the hardest part is keeping all of the parts lined up.
He ain't lyin'.
I lost count of the number of times I had the ejector, firing pin safety, hammer, and sear release lined up with a pin punch through the hole to keep them in place. That wasn't too hard, the hard part was not letting the pin punch fall out while trying to get the disconnector and sear into place. At which point, I'd lose my grasp on pin punch and all of the other parts would fall out.
I finally got those parts in place, and then spent another half hour getting the sear in place and held in by yet another pin punch.
This is where having four hands would have come in handy.
I finally got everything back in place, put the main spring and plunger placed into the Hogue main spring cup and got that in place. Now, to put in the grip pin.
This is where having six hands would come in handy. The Hogue piece came loose, the plunger and spring followed it and they all went into orbit.
At which point, the pin punch fell out and the hammer, sear release, ejector, and firing pin safety fell out. Again.
Sigh.
After finding the new main spring, and assembling that with the other main spring plunger and a spare Hogue piece I happened to have, I started again.
Finally, I got everything in place and put the sear pin and sideplate back on, followed by the grips.
Viola!

I've dry fired this a few times and there are no bad sounds from inside or weird sensations. The trigger action is smooth and it has double strike.
It's supposed to warm up later this week and I'll make an attempt to get to the range to see if and how it shoots.
I've retained the original trigger and sear and will be able to restore the gun to original condition if needed.
I still have to figure out what to do about matching the stainless firing pin retainer to the slide. There are a few ways to do it, but I'm looking for one that won't cost as much as the gun did.
I'm relatively sure that the people who built these guns at the factory had training, techniques, and tools to make it much easier than it was for me. The YouTube videos are helpful, but it takes a lot of dexterity to put the parts of the frame in properly. JohnHL is convinced that it requires people with finger joints that move in directions not normal for humans.
My thought is that there were several young children with small, but strong fingers, involved.
It can't be too hard, because I've been casting and eye towards a LGS that has a very clean 3914 and searching for a firing pin retainer.
OTOH, I have a very nice 3913 ...