M&P 45 Malfunction after Sear Modification

[HIKayaker]

I decided to do the M&P sear modification, altering the sear contact angle with the loop on the trigger bar. The filing of the sear and the polishing of the other contact points went well--and created a noticeable improvement in trigger smoothness, but it also created a new problem. I've not live fired it yet, but only dry fired to test it.

The M&P initially dry fired fine, but after about 10-12 cycles of the slide, there would be a slight delay between trigger pull and sear release of the striker. Later there would be a plastic sounding "thunk", rather than the normal metallic sound, and the striker would not release. In other words, the gun would not be able to fire.

After studying the mechanism with the slide removed, I determined that the trigger bar was drifting to the right (viewed from the top) and the loop on the trigger bar was passing to the right of the sear, failing to lift the sear.

It seems that the longest thin projection of the trigger bar sits in a horizontal slot in the housing block. If this were a hole, rather, than a slot, the trigger bar would be unable to drift to the right, preventing this malfunction.

Has anyone else encountered this malfunction? I think the trigger bar could be bent so that the parts that contact the sear would be further to the left, but it looks as if the magazine would just push it back to the right. Another solution might be to install a small projection about 1/16" thick to the grip frame where the trigger bar sits to keep the bar from drifting right.

Is there another solution that I am missing? Is this a common problem? My M&P never had this problem before I removed the housing block to perform the trigger mod. And as far I know nothing was handled rough enough to bend the trigger bar. From what I see, this could be a fairly common problem.

[mtnwinds]

When you filed the sear, it's possible that you created an angle that is allowing the trigger bar loop (popsicle) to slide out from under the sear.

Also, if you polished the popsicle, you may have rounded the edge of the loop so that it cannot remain under the sear.

It's also possible you've done both of the above.

[catcus-jack]

Originally Posted by HIKayaker

Is there another solution that I am missing? Is this a common problem? My M&P never had this problem before I removed the housing block to perform the trigger mod. And as far I know nothing was handled rough enough to bend the trigger bar. From what I see, this could be a fairly common problem.

Yes there is another solution send or take it to someone who knows what they are doing.
Yes this is a common problem it is caused by not knowing what you are doing.
The pistol functioned perfect until you worked on it so don't blame the pistol.

[shawn mccarver]

Originally Posted by catcus-jack

Yes there is another solution send or take it to someone who knows what they are doing.
Yes this is a common problem it is caused by not knowing what you are doing.
The pistol functioned perfect until you worked on it so don't blame the pistol.

What he said.

Why do people persist in ruining a perfectly good gun by making a questionable modification that absolutely does NOTHING to aid in better shooting than actual shooting practice would do? Amazing.

[kyf]

Wow.....where is the supportive, helpful group that offers suggestions not additional bashing. Ya, the guy made a mistake and probably feels like $h1t but common, if you can't offer help keep it to yourself.

[Lost Lake]

Easy fellas..... He's just trying to make his gun a bit better, and he did conduct a safety check.

Did you get the spring back on the front of the trigger bar? That spring pulls the trigger bar to the center of the gun, and under the sear.

During the cycle of the slide, there is a bump on the slide that pushes the bar to the right and out from under the sear.

Good luck!!

.

[standerson]

You are a harsh bunch.

I'd suggest you get a good S&W smith to take a look at it for you.

[forrestinmathews]

As a guy who broke his somewhat used trigger bar fiddling with it this is what I have to say: All of the "righteous" who don't dare to explore underneath the hood will never truly know how it works. So raspberries to you!

Rule 1: Don't change geometry if you can help it. If you do, you're venturing into uncharted territory and had better be ready to start back from stock.
Rule 2: Almost perfect is good enough. Pursuing that extra little bit when you're "in the zone" or "on the brink of perfection" is a gateway to over smithing and damnation. Going slow is good, but going too far still sucks.

What I have determined about the M&P via tinkering:
•The loop normally travels in and out from under the sear. This is how the gun disconnects between shots. Otherwise the striker would follow the slide and that's not gonna get you anywhere.
•The size and contour of the loop can be changed to decrease pre travel. Be sure that the loop can still get back under the sear to reset. Heat and quench to ensure the loop doesn't snap.
•Polish out imperfections in the loop. Don't change geometry.
•Be very careful in the polishing of the striker block disconnect "mountain". Take off too much height and you're getting light strikes because the striker block only partially disengages.
•Bending the trigger bar should be done carefully. You want enough tension for a positive reset, but not so much as to prevent disconnection.
•Have patience. Don't be afraid to walk away for a day and think about it. •Ignore blowhards that say I told you so now. Later they'll be commenting on your nice trigger. Leave them with their mediocre triggers and let them pay an "expert" through the nose.

[DanTana]

If I were you, I'd buy the Apex sear and put that in, and you'll probably be happier for it.

Sorry I posted the wrong part earlier, thanks Forrestinmatherws for pointing that out.
Here is the correct part:

http://www.midwayusa.com/product/976...p-45-acp-steel

I'm glad to hear everything worked out for you.

[randyr5]

I did the "Burwell" sear and striker block mod to my 9c. I had a chance to see an Apex sear and SB beforehand. I didn't go quite as aggressive as Apex on either of them. Polished trigger bar, striker, and smoothed out the channel that the SB rides in. The result is a smooth, somewhat lighter trigger with a slightly shorter reset that is 100% reliable.

When removing material from the sear, you have to be careful not to wind up with a slope from left to right. You must maintain the original left-to-right contour of the sear.

[forrestinmathews]

Originally Posted by DanTana

If I were you, I'd buy the Apex sear and put that in, and you'll probably be happier for it.

Apex Tactical Hard Sear S&W M&P 9mm Luger 357 Sig 40 S&W Steel

What he said except there's a hard sear just for the .45. Its a different part altogether.

I'll be sure to post a picture of the contour needed to eliminate the pre travel and still allow proper disconnect albeit with the FSS. I'm going to try to make it work with both a conventional and FSS trigger. Who knows if it will? Half the fun.

[HIKayaker]

Many thanks to everyone who posted to answer my questions. I do not have either great expertise or experience with M&Ps, but I very much appreciate those who do. Your suggestions are both helpful and appreciated.

So onto the next chapter.

This morning I finished an obedience title on my dog, and it was looking to be a good day. So I thought I'd take my M&P to the range this afternoon. It ate 102 rounds of my hand loads, (180g lead SWC over 10g Blue Dot. Don't laugh, it's what I've got left...) without a hiccup of the trigger mechanism. So, I am pleased with the trigger action, both feel and function. But I do have an Apex sear for the .45 on the way, ordered several days ago.

So whatever the problem was, it must have been related to manually racking the slide and dry firing repeatedly. I just couldn't see anything else that looked to be out of position or as if it needed to be adjusted, so I decided to see how my M&P trigger would work before and after going "bang". Turns out it was a very good day indeed.

Oh yeah, anyone ever favorably comment on how easy M&Ps are to clean?

Thanks again. Answers like these are what this forum is for.

[Rastoff]

My dad used to say, "To learn how to shuffle, you have to ruin a few decks of cards." Don't worry about it. The M&P is a robust design that is easy to work on. You haven't done anything that is hazardous. The worst that can happen by altering the front of the sear is that it won't fire.

You didn't alter the back of the sear did you?

I suspect, like some others have said, you inadvertently altered the angle and have a little left-to-right slope on the sear now. Ordering the new Apex sear is the right thing to do.

Originally Posted by HIKayaker

So whatever the problem was, it must have been related to manually racking the slide and dry firing repeatedly.

If this is the case then there is something wrong with your gun. Manually racking the slide and dry firing it will not cause any harm or malfunction to the gun. So, if it did malfunction due to manual manipulation, it may be the alteration to the sear that caused it.


Here is how the trigger works: Smith & Wesson: How the M&P Trigger Works - YouTube

As you can see from my video, the trigger bar HAS to move to the right for the gun to function properly. Making any modification to prevent this travel could cause the gun to malfunction in an alarming way.