Mod 639 Ambi-safety/de-cock

[Shaunogun]

Just acquired a 639 and have seen some posts regarding upgrading the ambi-thumb-latch to gen-3 to be rid of the screw issues.
Can someone confirm that this can even be done?
I have also purchased a couple of SS slides from a local gun shop that are left-over from destroyed pro-hibs, (makes me want to cry to even say that here) one has left side only latch c/w Novak sight, and other has gen-3 ambi set-up with guarded adjustable sight. I think I could just switch slides around and leave the O.E.M. set-up alone, but was curious if anyone had made the switch.
Thanks in advance, Shaun

[taxifolia]

Not sure exactly what you mean - do you want to retain the ambi, but just replace complete decocker body with the style that has retention pin for right lever instead of screw ? If so, I understand from a friend that the decocker body it fitted to the slide. He said "Remember that the decocker is a fitted part on the 2nd gen guns and one from Numrich may not work".

If all you want to do is get rid of the right side lever, I did that - see my post today "A couple nice ones".

[Shaunogun]

I was hoping to retain the ambi, just ditch the screw. I'm not hating it that much, it's a great looking gun regardless, just was curious.
I'm heading to your other post now to have a read.
Thanks for the reply.

[357larry]

A good person to ask is Nyteman 44 here on this forum. He has quite a bit of knowledge in this area. He recently worked over a slide from a 5906 with adjustable sights for me for use on my 639 frame. He does great work.

[Shaunogun]

Thank you. One of the spare slides I picked up is from a 5906. I'll contact him for details.

[squidsix]

It works. Caveat: I have used the 4506 safety on a 645, and it worked.
The assembly is virtually identical inside.

[Shaunogun]

Thanks all, visually it sure looks identical but was a little concerned about the "fit to" scenario. Tolerences must be close, but if they are "slide specific" there might be an issue. I can mic them anyway. Guess I'll find out.

[grif684]

It's a straight swap, I am left handed and put third gen safeties on several of my gen two autos that were not equipped with ambi safeties, and I always use the no screw third gen models.......

[SG-688]

Changing the safety - or even switching slides - may require fitting, but the safety is not the part that is modified.

The fitting point is the sear release lever - part #6103 in this diagram.

Assemble, conduct 2 step test for safety function, take it all apart, lightly file the lever, ...repeat until it passes both steps.

May require replacement of the lever if the lever is already too short.

Pain in neck since you are working blind, unlike with a 1911 where you can see the safety to sear fit, but it does not have to be as precise as with a 1911.

You must first understand the two step test.

[alettoco]

t...............

[Fastbolt]

The 3rd gen manual safety/decock assembly can be installed in 2nd gen guns ... but ...

The fit & function of the new assembly should naturally be checked to make sure it operates correctly in the new slide, and the decocking "timing" needs to be checked.

This used to be done by "eyeball", while performing the decocking action, but nowadays armorers are given 3 numbered drill bits to use as Go/No-Go gauges (the non-cutting ends used as the "gauges"). More precise and easier to do (not to mention it's easier to train an armorer to use the gauges during the class ).

It's not uncommon for the existing sear release lever to require replacement when a new manual safety assembly is installed in any particular slide, and it's a "fitted" part. Fitting is done by filing the foot of the lever, while maintaining the original factory angle and bevel, until it provides for the correct decocking "timing". When you're decocking & dropping the hammer over a live round, you want the operation to go as designed and intended, right?

This ought to be checked and done by a gunsmith familiar with S&W TDA pistols, or a S&W armorer, so the safe functioning & operation of the pistol is maintained.

Another issue that can arise is if someone mixes up the plungers & levers in the new manual safety. There's an ambi lever plunger & spring and a 'body' plunger & spring in the ambi manual safety.

There are 2 different vintages of ambi lever plungers & levers (which have to match).

The body plunger & spring are different than the ambi parts.

If the lever plunger spring is mixed up with the body plunger spring, the gun can 'decock' with each shot, and you may have a single shot gun with the safety going to the On-Safe/Decock position under the recoil of the gun being fired. (I know of it happening with a local agency some years ago, although the mix-up was fortunately discovered at the qual range and corrected before someone really had to use their weapons. )

If you mix up the plungers the decocking effort may be difficult & rough, and the wrong plunger might eventually cause wear or damage inside the slide.

FWIW, just replacing the slide would still require the decocking timing being checked (since it's still a "new" manual safety as far as the sear release lever in the frame is concerned) ... and then you still have to make sure the rest of the new parts work together properly and provide for normal function.

[SG-688]

Originally Posted by Fastbolt

....

This used to be done by "eyeball", while performing the decocking action, but nowadays armorers are given 3 numbered drill bits to use as Go/No-Go gauges (the non-cutting ends used as the "gauges"). More precise and easier to do (not to mention it's easier to train an armorer to use the gauges during the class ).

....

Thanks for the update. I was trained during the "eyeball era" ... even before extractor gauges.

This is a rarely understood topic here. Ought to be a sticky on it.

[Fastbolt]

Originally Posted by SG-688

Thanks for the update. I was trained during the "eyeball era" ... even before extractor gauges.

This is a rarely understood topic here. Ought to be a sticky on it.

I guess the academy's armorer training folks eventually decided it wasn't as consistently easy to try and teach new armorers how to slowly manipulate the lever(s) by hand, stopping at the moment of decocking, and then snapping the hammer a few times (on the spurred hammer guns) to check for the necessary additional lever downward movement after decocking had occurred.

Easier to teach brand new students... and a more effective use of class time ... to use "gauges" to check the timing. Probably an extension of how they were first showing armorers they could use the tips of a couple of the different size cup-end pin punches as ad-hoc gauges to check the spurless hammer guns (since the hammers couldn't as easily be pulled and snapped to check for the extra lever movement).

The new sear release levers are made much closer to the tighter range of tolerances found in the newer 3rd gen's, making it easier & faster to fit a new lever ... (unlike the really overly long levers that sometimes required a LOT of filing & checking before working properly in a particular gun).

If you'd like, I could PM you some info about the new numbered drill bit "gauges" being used to check the decocking timing.

[TAROMAN]

I went through this a while back with fitting a 2nd slide to my 639 so I'd have a fixed sight and adjustable sight one.
Had the new slide Black-T coated, too.
That slide came with an ambi decocker. The right side lever had no screw, it was held by a spring pin arrangement:

I swapped in a single side one, but the decocker wouldn't work properly.
Fastbolt explained it was the lever fitting issue.
Local gunsmith could not comprehend it (he's a rifle specialist).
So, I shipped the gun and both slides to S&W with a letter explaining the issue.
Came back with only a note taped in the box:

"Replaced lever N/C"

Both slides run perfect now. THAT'S service!

[Smee78]

Wow this is some great info here, thanks everyone. Taroman love your pics, they look great.

[taxifolia]

Originally Posted by Smee78

Wow this is some great info here, that everyone. Taroman love your pics, they look great.

I especially like the first one - the SS slide