When it comes to the "parts is parts" manner of how may of the 3rd gen parts can drop into the guns, there's still the possibility that a given part (like the standard manual safety) might not drop into some particular gun and offer optimal fit & function. That's when an armorer can try a different part to get one that fits & works normally in that particular gun.
There was one time when I slipped a standard (single lever) manual safety into an early production 6906, considering replacing the ambi assembly (since it was chewing up the linings of my work coats when I carried it in an open top holster). The manual safety I had in my parts boxes turned out to be just a bit too loose in that particular 6906 for my liking, so I didn't make the switch. (I didn't have any other standard safeties in my parts collection, and I didn't feel strongly enough about it to order one. I switched to a leather holster that covered the ambi lever ... only to find it was also the sharply cornered early 3rd gen rear sight that was causing just as much damage to my coat linings.
)
I have, however, made the switch in other 3rd gen guns, using other manual safeties (standard & ambi), without any issue. Just depends.
One other thing that needs to be checked once the new manual safety is installed is the decocking "timing" .
The top of the sear release lever indexes off the bottom of the cylindrical body in order to perform its decocking function. Subtle tolerance differences being what they are when you combine different frames, slides, manual safety bodies and sear release levers, often a new sear release lever may have to be installed and fitted.
The timing used to be checked by eyeball to gauge when the lever dropped the hammer, but nowadays armorers are taught to use the non-cutting ends of 3 different numbered metal drill bits (as Go/No-Go gauges, of a sort) to determine when the decocking timing is within the normal range.
Fitting the lever isn't particularly difficult,
if you know what you're doing, since it's something that really requires knowledge of disassembling the frame (to remove and install the sear release lever), as well as being able to file the foot of the release lever while maintaining the
original angle of the bottom of the bottom of the foot (which is critical, as it engages and moves the sear nose during decocking).
One too many file strokes, though, and the lever can be ruined and you start again with another lever.
It used to be harder with the older guns and older levers, with the older & looser tolerances, as the levers were machined really longer than necessary (for fitting). The newer levers seem to require less filing. (Which is handy, since checking for the right timing requires complete reassembly of the guns in order to check it - and is one of the reasons many armorers cut down older grips to just a 'backstrap', so they could be used instead of installing the full grips. This is why the 2nd gen bakstraps were popular among armorers, since they could be used as they were for this function, instead of cutting away 3rd gen grips to "make" one.
)
Filing the lever's foot (meaning maybe only 1-2 strokes) & then reassembly of the gun and checking the timing ... then disassembling, filing another stroke (maybe two) ... then reassembling & checking again ... it can get tedious. Sometimes it's that
single extra file stroke, because you're tired of all the reassembling & disassembling, is what becomes that one-too-many-file-strokes and makes you start over with another lever.
You might get lucky and have an occasional safety drop into any particular gun and find the existing lever still provides an acceptable decocking timing, but it's best to have it checked so the gun functions in the safe, proper manner in which its designed to operate. This is where a gunsmith familiar with S&W TDA pistols, the factory techs or an armorer (if you know one), can save you money, time, frustration and some potential grief.
It's also important not to mix up the plungers and springs in the ambi manual safety! The heavy body plunger spring and the rounded body plunger are needed for the manual safety. Mixing up the heavy body plunger spring with the lighter weight spring used for the ambi lever can result in "decocking" each time the gun is fired.
Not good. It can make it essentially a single shot pistol, with the safety having to be lifted upward between shots.
Also, mixing up the semi-rounded head (older style) ambi lever plunger, or the newer-style flat headed plunger, with the fully rounded head body plunger can make for really nasty & heavy decocking lever movement, as well as digging into the machined surface inside the slide where the body plunger runs during decocking.
Just my thoughts.
If you lived close to me I'd offer to install whatever manual safety you bought and check it for you, and then check/install/fit a new sear release lever (if needed). The sear release lever is a whopping $2 part(retail), and I've collected a fair number of them during armorer classes over the years.
If you're going out to the factory, I'd check to see if they have any parts in-stock (they aren't replacing their 3rd gen parts inventory as often at this time), and see if they can do the installation & function/fit check for you.
S&W 3913 Right-handed safety
3rd gen smiths
Linear Mode
