Broken SW99C rear sight

I dropped my SW99 [#120212, .40 S&W] and it landed directly on the side of the rear sight. The plastic sight body internal threads appear stripped and the part that holds the adjustment screw in place has sheared on one side. The sight is FUBAR. As usual, the S&W Instruction Manual doesn't have a parts list or assembly diagram so I can't tell what I'm dealing with.
Where is there a diagram that shows the rear sight parts and how they are put together ?
How do I remove the slide end cap to get at /remove the part that holds the adjustment screw ?
Where can I buy a complete replacement rear sight assembly ?

BROWNELLS : Schematics Home - World's Largest Supplier of Firearm Accessories, Gun Parts and Gunsmithing Tools
(EDIT)
You can order either from here or the factory.
Your misfortune however gives you an opportunity to upgrade the sights to materials and construction more durable?

The good news is that you don't have to remove the slide end cap.

The rear sight base is held in position by the rear sight plunger (on the right side of the base). The plunger has a machined slot on the top in which the edge of the windage screw slips. (This is done by depressing the plunger and installing the sight base from the left until the plunger can be released so the slot catches the bottom edge of the windage screw.) The plunger holding the edge of the windage screw is what holds the sight base in the dovetail.

The plunger is the 'weak link' in this sight design. An impact can cause one or the other of the edges of the slot on top of the plunger head to break off. This can result in the windage screw not being held in position.

The rear sight base is removed by using the flat tip of a small regular screwdriver to depress the plunger (outer lip of slot, or the broken edge of same if the right side broke off) so the sear sight base can be pushed to the left and out of the dovetail. Carefully release the plunger and remove it and its spring from the plunger hole in the slide. (Safety glasses can be handy if the plunger unexpectedly slips free.)

If the sight base has shifted to the right, over the top of the plunger, then you can't get at the plunger to depress it. If that happens the windage screw must be removed (Note the left hand thread). This will lose the sight adjustment because the windage screw must now be reinstalled and then the sight re-zeroed when the new plunger and spring are installed and the sight base is reinstalled in the slide.

In the armorer classes I've attended for the SW99/P99 series, I think someone has mistakenly tried to either remove the rear sight to the right, or install it from the right, in each class. This caused the sight to slide completely over the top of the rear sight plunger and completely' capture' the plunger ... requiring the removal of the windage screw in order to be able to remove the rear sight base and free the plunger.

I've had to replace a couple of rear sight plungers because of damage when the guns were dropped by our folks. I've also heard that aggressively buckling a seat belt can break the plunger slot if the buckle is hit against the rear sight base of a holstered gun.

After the first time one of our folks dropped his gun down some concrete stairs and damaged the plastic rear sight, as well as breaking the top of the rear sight plunger, I decided to keep a few extra bases, plungers & springs on hand.

Fastbolt said:

..........
The plunger is the 'weak link' in this sight design. An impact can cause one or the other of the edges of the slot on top of the plunger head to break off. This can result in the windage screw not being held in position.

Click to expand...

Thanks Fastbolt for the detail description of my problem, sight operation and solution. [I also dropped my SW99 on concrete] Knowing the adjustment screw is left handed [go figure] I find only the plunger is in need of replacement as you noted. Now I'll have to find a new one.

Spotteddog said:

BROWNELLS : Schematics Home - World's Largest Supplier of Firearm Accessories, Gun Parts and Gunsmithing Tools
(EDIT) You can order either from here or the factory.
Your misfortune however gives you an opportunity to upgrade the sights to materials and construction more durable?

Click to expand...

Unfortunately Brownells doesn't list replacement parts for the SW99 series so guess I"ll have to make a call to S&W after the holiday.....

De nada.

S&W can send you the part. They have the stock plunger provided by Walther for the stock plastic rear sight base (and which is also used for the night sights offered by S&W for the SW99/990L's). If the customer service folks can't locate the part number (but they ought to be able to do so) ask to be transferred to the Walther America parts extension (different building on the property), but you'll have to ask for the right part number.

The S&W SW99/990L part numbers should be these, but ask the customer service person to double check for applicability and any revisions:
#264190000 $3.62 X REAR SIGHT PLUNGER
#264180000 $2.42 X REAR SIGHT PLUNGER SPRING

There is a different pin used for the Walther steel rear sight, although I haven't ordered any of those for comparison.
http://www.carlwalther.com/views/p99_c_as_2765101.pdf

Fastbolt,
Exactly how this unfolded is the strong suit of this place!
Thank You, for sharing your expertise and knowledge!
(This Place is Great!)

You're welcome.

Fortunately, this was a simple enough issue.

FYI, as an alternative to from S&W, I've discovered Midway stocks the rear sight plunger but they are currently out of stock and are on back order. Cost listed is $4.19
MidwayUSA - Smith & Wesson Rear Sight Plunger S&W SW999, SW9940, SW9945, SW9909C, SW990L40, SW990L9, SW990L40

I called S&W and they sent me a replacement plunger at no charge. Can't beat S&W Customer Service !

Any problem getting the plunger installed?

Fastbolt said:

Any problem getting the plunger installed?

Click to expand...

Nope, dropped right in. It certainly is the weakest link.

Yeah, back before S&W was starting to think about designing their own plastic gun, I was told that they were considering changing their own 99 slide to use a standard dovetail cut to permit use of the regular press fit rear sight bases as are used on their other guns.

As I mentioned earlier, as long as you remove & install the rear sight base in the proper manner (so you don't capture the plunger under the base and have to unscrew the windage screw), it's simple enough.