So I just finished installing an APEX FSS and polymer trigger on my new M&P 40. Figured I would share my thoughts and difficulties I ran into. Sorry I didn't take pictures. I originally was going to but missed some steps so just said forget about it.

The kit was delayed a bit by USPS so I started with the rear sight removal. I figured this was the step that would have the most potential for problems. I took a 1/16th angled hex driver and tried to loosen it. At first it seemed pretty tight but it came out without much trouble. There was indeed a dot of red loctite on the side of the screw. I noticed some people mention to use a soldering iron, flame or heatgun to loosen it but I didn't have to. As a side note.. you may want to remove the striker assembly and striker locking plate as they have some plastic parts that could melt it they got too hot.

So with the screw removed, I put some cardstock from a folder I had on the sides of the slide and put it in a vise. I had ordered a nylon punch from Brownells but it had not arrived yet so I tried with a plastic marker I had. I then hit it with a brass hammer. At first I tried putting it against the bottom-most shelf of the sight where it meets the slide. This just chewed into the marker which was not surprising. I read online to position above that and you can see that there is a decent amount of metal there to place a punch. I started light and gradually increased the power of the hits. Would not budge. The plastic of the marker wasn't so strong so I switched to a wooden dowel rod. Also would not budge. Switched to a regular hammer you would use for nails. Wasn't budging but after a particularly strong whack.. it finally broke free. After that was some lighter tapping to get it off (being careful to capture the striker block spring and cover). There was not loctite under the sight... just very tightly fitted.

Then I waited for the APEX kit. When it arrived I had watched the APEX youtube video and also an AGI gunsmithing video on the M&P. After standard disassembly of the M&P, you will want to remove the slide stop. The APEX video does not explicitly mention this and he does it without saying anything in the vid. You then drive out the trigger roll pin and the trigger pin. Then drive out the rear roll pin. These were straightforward with a 1/8th punch. You then lift out the rear block with a screwdriver and once it is out, you can slip it free of the trigger bar.

I then removed the front block and then the trigger with the slide catch. Next step is driving out the pin the holds the trigger bar to the trigger. I don't know what size the punch is.. maybe 1/16th. They fell apart at this stage and I kinda worried for a second that I should have paid attention to their orientation. Basically... if you looked down at them as if you were looking down at the top of the gun... the little shiny loop on the back of the trigger bar should be on the left.

The polymer trigger I got from APEX already had the pin mostly seated... it was pretty much ready to put the trigger bar in and tap a little bit to lock it in. There is some wiggle room for the bar when you push it into the trigger... so you should play with it and try to see where it needs to be for the hole to line up. When you hit the pin with a punch/hammer... the side where you can see the hole will be down.. so you kind of do it blind. It went in easy for me.. but a spent a few minutes getting comfortable about how it lined up.

Also... I think in one of the APEX videos... they suggest using a vise to press it in. This might be much easier/foolproof... but I didn't want to spend the time to get flat plates into my vise.
Next step is putting the trigger, slide catch and trigger bar spring together with the provided slave pin. One thing that was tricky to figure out was which way to put the spring. I put the small side on the trigger bar and the wider side on the slave pin. I am pretty sure that is correct. You also have a choice of orientation when you hook the spring to the trigger bar... the sharp end of the spring can go up or down... I put it up as that seemed harder to slip off somehow. It might not even matter as it probably won't slip off when under tension anyway.

Once everything is lined up on the slave pin... you put it into the receiver and put the front block on top. Then you drive the non-roll pin trigger pin through, pushing out the slave pin. This took some wiggling and the APEX video shows some of the places you might need to wiggle to get it through. He also mentions the spring getting stuck. This did not happen but I do not have a hooked dental pick and I think it would be hard to get around this without a special tool like a dental pick. There is very little room to get something in there and I couldn't think what tool I would have used if it did bind.

I then went ahead and drove in the front roll pin and moved onto the rear and final part. You slip out the pin that is touching the ejector from right to left. I heard that older model M&P 40s had ejectors that would simply fall out but the M&P 45s had one that slid into the front. My 40 seems to have a similar configuration as the 45s.

The sear can be easily removed but it wouldn't be a bad idea to have small tweezers to get the spring and pin back in. Doable without.. but no stress at all with tweezers. Put the new sear in and depress it to put the ejector and pin back. Put the rear block back in the gun and drive in the roll pin.
And done! Luckily function testing the gun was fine. Did not have to readjust the trigger bar loop.

Oh... totally forgot the final step which was getting back to the slide. I saw a video by 10-8 performance discussion the installation of sights. He seemed to feel it was best to have a rear sight not quite so tight. He files down the back of the sight's dovetail to get it in a bit easier.

I don't have a triangular file... only a flat one... so I filed down the front dovetail (the one that is closer to the barrel when installed). When I did this... I wondered why he was using a triangular file on the rear dovetail as that seemed trickier. I realized why after installing but I will get to that.

I ended up filing maybe 10 strokes at a time and then seeing where it would fit. Before starting... it got less than halfway before sticking. I kept doing 10 strokes at a time and it didn't seem to move too much until I hit a point where filing would make it move a good millimeter. So be careful feeling that you arent making progress and going too fast.

I got it where it was about 4 millimeters away from final position when pressing it firmly into position. Then... when pushing as hard as I could with my fingers it was about 2 millimeters from final position.

This is when I realized why you might not want to file the front... it the polish mark will be visible if you look at it from the front. Not too big of a deal but I didn't want the shiny metal showing. I bought a bluing pen. Was a little worried that it might be a stainless steel sight but I think it was not as the bluing did seem to take. The shiniest part took maybe 10 minutes with maybe 30 applications to get decently dark.

I would estimate that I gave it around 150 strokes with my file to get it to this point.

Once it looked reasonably blued again... I pushed it in as hard as I could and just a few taps with the wooden dowel rod got it centered. Then locked down the lock screw and all was good.

Time will tell if I took too much off of the sight when filing. I think it is good but who knows. If it does slip I may add blue loctite and if that doesn't work... I could use red like the 10-8 guy suggests.

Wow, I cheated, I sent my gun to APEX.

A good tool for handgun owners would be a sight pusher. This one is a little crude, but it works with most handguns and is about 1/4 the price of a sight pusher dedicated for one pistol. It makes sight removal painless and it works much better out at the range to adjust sights than a hammer and brass punch (I've done both). On Sigs, this is mandatory because if you thought the S&W sights were tight, you'd have thought the Sig sights were welded on.

One of the things you should be on the lookout for with a newly installed FSS trigger kit would be "dead trigger". This symptom can be cured with an adjustment to the trigger bar loop. A very small adjustment to the opening is all that is needed.

Congratulations on your new FSS kit. You now have a new gun

Thanks for sharing your experience. I put the FSS trigger kit in mine last week. It was much easier than I expected. Even adjusting the trigger bar loop was no big deal.

I put about 200 rounds through it last weekend. What a huge improvement it was!

I'm very happy.

When I installed the aluminum trigger, I couldn't get its pin to budge at all without putting it in a vise. Apparently it's much easier with the polymer trigger.

After doing 7 of these kits, I can knock them out in about 20 minutes start to finish, including a gentle wool wheel polish of the apex parts.

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Matt H.

My first one took me about 4 1/2 hours but I tried all combination of the sear and trigger return spring. I settled on the supplied springs because the trigger was so precise after installation, I didn't want it lower than 5lbs.
I'm sure I could do follow-on installs a lot quicker, but it seem to me that each of the how-to videos misses a couple of things.