I've done some basic modifications to a 5906 to teach myself about pistols. I've taken it to the range 3 times since the modifications with no problems until today. I fired about 100 rounds through it and near the end I had a definite double fire.

I don't know if my finger came off the trigger and reset it, allowing the double fire to occur. Or, if my finger stayed down and the gun fired the second round without my help.

Here's a list of the modifications I've made to the gun. The single action pulls at almost exactly 4 pounds, it was pulling closer to 5 pounds when I bought the gun a couple of months ago.

Mods:
Installed Wolff Reduced Power 16 pound hammer spring
Installed Wolff 2.5 pound trigger return spring
Stoned and polished trigger drawbar
Stoned and polished lower frame contact rails
Stoned and polished the central rail on the slide

I stripped the entire lower frame and reassembled it to get those tasks done.

I've read that it's possible for the shooter to induce a double fire and the trigger is light and crisp after installing the springs, so I'm hoping it's me not following through and not holding the trigger through the recoil.

I did not sand or attempt to polish the hammer, sear or any of the other trigger contact points aside from the drawbar.

Let me know what ya'll think
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Can you measure the SA trigger pull? SA pull weight is often an indicator of other issues.

If this is the gun double firing, I would guess it has something to do with the drawbar "stoning", or the aftermarket trigger return spring. When the trigger return spring is lightened, there can be a negative affect on proper disconnect.

I would also visually inspect the SA notches on the hammer, and the sear for any obvious damage,(use a magnifier) and check the disconnector for proper movement and function.

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Ret. LE, FA Instr, S&W Armorer

The single action pull measures almost right at 4 pounds, so it didn't seem dangerously low.

The trigger return springs were the absolute lowest Wolff sold and I'm hoping that's the cause.

I know I didn't mess with the gun's SA notches but I have no idea what was done before I bought the gun

It's also possible that I didn't put the disconnector back in properly.

I'll tear it down and check the function and notches.
Thanks!

Anybody else's input also welcome

The factory spec for the SA is a 4 pound minimum....and the notes in the armorer's manual specifically advise not to alter/modify the trigger return spring.

This spring's role is multifunctional with respect to the position and tension on the drawbar, and the drawbar's interface with the sear and disconnector.

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Ret. LE, FA Instr, S&W Armorer

Ok, I can for sure change back to the factory spring and see if that's the case. I'm going to change the spring first thing, and check the other parts to look for damage.

Thanks so much for your input Armorer!