I'm in the middle of installing the polymer trigger in my FS M&P. I'm ready to attach the spring to the trigger bar and trigger. I called Apex earlier with a couple questions and asked whether I needed to use this spring or if I could use the factory spring. She said that I had to use this one as the factory one might cause problems. This spring does not match the springs in the video. They mention a big loop and small loop and the spring that came with the trigger does not have any loops and looks pretty flimsy. I've attached a picture of the factory spring and the one that came with the trigger. Can anyone confirm that I'm really supposed to use this little spring? I tried to call them back but even though it was within their business hours, they must have closed early, I couldn't reach anyone. Am I confused and this spring is for something else?

Attached Images

spring.jpg (53.2 KB, 102 views)

At least one of us is, maybe both. The spring on the left looks like a stock trigger spring, which is an EXTENSION SPRING. The spring on the right is a COMPRESSION SPRING. Picture is too fuzzy for me to be sure what it is.

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Science plus Art

It was hard to get it any clearer and be able to see the spring, it's so small. The one on the right is what came with the trigger in the package. I thought that it was supposed to replace the trigger spring but I'm guessing no. I don't see any mention of it in the AEK video.

The one on the left is the trigger spring. the one on the right looks like the sear plunger spring. You should have another spring that looks like the one on the left. That's the one to be used on the trigger.

Did you buy ONLY the trigger or did you buy the FSS or DC/AEK kit?

That spring is either the sear spring or possibly the striker block.

If all you bought was the poly trigger, it's the sear spring.

https://store.apextactical.com/WebDi...Details/191817

The spring on the right is the only spring that came with the trigger. There was the trigger, the small spring and the yellow slave pin, that's all. Anyone have trouble getting the locking block back in?

This is what you purchased....

In The Package
1 ea. Polymer Action Enhancement Trigger
1 ea. Heavy Duty Sear Spring
1 ea. Slave pin (assists with installation of trigger return spring)

You can use your trigger return spring but it might lighten up the trigger pull.

The lock(or trigger block) are a tight fit. This is the sequence I use, put the slave pin through the slide lock, trigger, and trigger return spring (assuming the trigger spring is already hooked into the trigger bar (long thing with the loop on the end). Slide the end of the trigger bar under the sear and lower the trigger and slide lock into place. Then put the locking block into place making sure you don't displace the little "L" shaped spring that keeps the takedown lever from flopping around. Put the trigger pivot pin in with hand pressure only, if you have difficulty don't under any circumstances hammer it in. If everything is correctly aligned it will slide all the way through easily. I say this because I've repaired a number of M&P's with broken parts because of this. It is tough to get everything aligned and make sure when you get the pin in that the spring didn't pop out of place and the pin not go through the upper loop. (seen that more than once). Good luck, it's not hard, just need patience.

The video that is supposed to go with this kit does not mention anything about the sear spring. I just need to find a video that explains how to swap this. Finally got the locking block in so at least that's all set.

That spring on the right is a sear spring. It is what pushes up on the sear to keep it raised to catch the striker, until you pull the trigger to rock the sear (against that sear spring) to fire.

It is nothing at all like the striker block spring.

I got everything put back together but did not swap the spring to see if it worked. I opened the trigger bar loop but had to open it a lot. I bought a feeler gauge and it did not even go big enough. I opened it to .025 and at that point the trigger worked. Put the rear pin back in all the way and now the trigger doesn't work at all. Would the sear spring cause this? The trigger works if I pull up on the slide a little bit. According to the video, this supposedly meant I didn't need to make that much of an adjustment. I'm afraid to open the trigger bar loop too much.

I had already tried to hammer it in a bit and knew something wasn't right so I stopped. The slave pin was a little off and that was stopping it from lining up. I got it fixed and the pin slid right in. I also found something in another video that suggests wiggling the trigger a bit and that helped get it seated correctly.

Ok so I installed the sear spring, opened the loop a little more and the trigger worked with the pin partially installed. Put the pin back in all the way and the trigger stops working again. Any ideas?

Took the pin out again and put the slide back on and the trigger works fine. I put the punch thru the hole and the trigger works every 2nd or 3rd pull.

Try closing the loop down a bit, it may sound counter intuitive but part of the timing sequence is pushing the striker block out of the way, if the loop is opened too much the block won't allow the striker to fall. Old picture as an example, I've never measured the gap, just closed it down until it wouldn't allow the sear to release the striker and then opened it up a bit.

Attached Images

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I tried closing it back down and it made it worse, I may have gone too far back. In the video, he has to adjust it to 16 thousands, I'm "assuming" on the gauge that means .016. What I don't understand is why having the pin in is making the difference. I closed it down a little and at about .020, it fires consistently with the slide on and no pin installed. I put the punch thru the hole and it fired consistently. Once I install the pin again, it does not fire.

Ok, so it appears that the reason it is firing with the pin out is because the slide is lifted slightly. If I hold the slide tight against the frame, it doesn't fire at all even with no pin in. So does that mean I need to open it back up a little?

Yes, you probably went to far.

I wasn't sure how far was ok to open it up. I called Apex back and she said it varies quite a bit, some people have to go .05. It was working without the pin but with the punch in the hole at .025 so I need to go a little further and keep trying it. Once I've got it to it dry fires reliably, I will test it at the range. What is a good number of rounds to fire to test it? If I put 100-150 thru it with no problems is it safe to say that's a good test?

With the number of issues that you had, I would shoot at least 150-200 rounds through it.
More is obviously better and in this case more would definitely make you feel better about it going bang every time you pulled the trigger.

Got it working right now. The feeler gauge didn't have enough feelers so I had to combine 3 of them and open it to .054 but it is working consistently now. I just didn't think I'd have to open it as much based on the video. I'm going to do some more dry firing tonight and then take it to the range tomorrow to test it out. Thanks to everyone for the help! I'm glad that I did it myself and might look into learning more. I kind of enjoyed it.

Enjoy your Shield...

Make sure the trigger bar loop has enough room to reset back under the sear. With the slide off and an empty mag in (if you have the mag disconnect version), pull the trigger and slide the trigger bar loop away from under the sear toward the right wall of the gun. That's what happens when the slide moves back.

Now slowly release your finger from the trigger and see when the trigger bar loop slips back under the sear. Make sure it slips back easily with room left over. If it doesn't reset or it resets way at the end of the trigger return, you might end up with a dead trigger also.