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light primer strike

This is a discussion on light primer strike within the MP Gunsmithing forums, part of the Smith & Wesson MP Forum category; had my first light primer strike today and can't figure out if it was a fluke or if I need to adjust something on my ...

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Old September 28th, 2014, 02:30 PM   #1
Join Date: Sep 2014
Location: iowa
Posts: 36
light primer strike

had my first light primer strike today and can't figure out if it was a fluke or if I need to adjust something on my gun. Malfunction happened around the 400 round mark and the gun had been flawless before that. The gun has the APEX DCAEK and AEK in it. Ammo that malfunctioned was ZQI 123gr.

I put the DCAEK kit in at the 100rd mark and the AEK in at 270rds. I did open the loop up to .016 but still only have around .005 overtravel(measured at the top right of the trigger). Should I open the loop up a bit more or could it just be a fluke with the ammo? I've ran a total of 455rds through the gun with 185rds since the AEK install and this has been the only misfire.

I should also note I have a small issue with the AEK trigger. When I installed it I got a little rough driving the pin in and the pivot pin gouged and cracked the trigger right above the pivot pin hole. The trigger does rock a bit side to side due to the pin hole being slightly out of round and cracked at the top. Could this extra play maybe have caused the trigger bar to not engage the sear properly? I do have a new trigger coming and should have it in by the end of the week.

ETA. I pulled the slide off and there is a silver colored mark on the back of the sear so I'm wondering if the striker is dragging across the top of the sear. Probably need to open the trigger bar loop up a bit more?

Last edited by gunner76; September 28th, 2014 at 04:52 PM.
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Old September 28th, 2014, 05:15 PM   #2
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Location: Kingston, ON
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The mark on the back of the sear is normal. The trigger wouldn't stop the striker. Have you cleaned the striker? I've found that with my MP FS that if it gets real dirty that the striker always fails first. Secondly, if you do clean it make sure you put it back in dry. No oil or anything. Oil or grease will cause excess carbon to stick to it. I pull the striker out and clean it up then use a pipe cleaner folded over to clean up te striker channel and the hole. Hope this is your issue because it's an easy fix.

Don't screw with your trigger bar. Opening it up won't affect the striker. If you open it up too much you'll end up with a dead trigger. As long as te trigger breaks then the parts in the frame half of the gun are working fine. Your trouble is likely with the striker.

Last edited by Kandress; September 28th, 2014 at 05:17 PM.
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Old September 28th, 2014, 05:19 PM   #3
Join Date: Sep 2014
Location: iowa
Posts: 36
I haven't touched the striker yet. I figured since the gun only has a little over 400rds through it and I haven't put any oil near the striker that it wouldn't need to be cleaned. When I strip the gun down to put the new AEK in I'll pull the striker out and see if it's dirty.
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Old October 20th, 2014, 06:11 PM   #4
Join Date: Sep 2014
Location: iowa
Posts: 36
still having issues. I've put the stock two piece trigger back in, cleaned the striker channel(wasn't dirty anyway), put in a Glock 5.5lb striker spring since Speed shooters is out of the M&P extra power springs and nothing makes a difference. I checked the APEX USB and it does not have any marks that would indicate the striker contacting it as it slams forward.

Right now the only ammo that is giving me failure to fire problems with light dimples on the primer is ZQ1 so I'm going to stop using that stuff. I'm also getting varying hits on S&B and Gold Dot ammo but they all go off.

What gets me is how can I go from good solid hits to stuff that's really light. Some of the S&B and Gold Dot casings have hits that are just as light as the ZQ1 and they all went off. Here is a photo of some of the Gold Dot casings next to the factory fired Win case.

I was reading on another forum that a guy was having similar problems and it ended up being a sticky extractor not allow the casing to fully seat in the chamber, could this be a reason?

ETA. Federal ammo all has really good hits on them.

Or maybe it could just be the primers smearing during the unlocking of the barrel and covering up the indentation a bit?
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Old October 21st, 2014, 02:14 AM   #5
Join Date: Oct 2012
Location: Virginia
Posts: 256
Just my experiences with two FS M&Ps.

The 9MM had the light strike issue first. The light strikes were in the center of the primer. I replaced the striker spring with a heavier Glock spring. Didn't fix it. I checked/cleaned the striker/liner. Wasn't dirty and didn't fix it. I blamed the primers and stopped using the Tula primers. Didn't fix the problem.

I swapped the factory parts from the FS .357 SIG to the FS 9MM and put the APEX parts in the FS .357 SIG.

The 9MM began to work. The .357 SIG gun began to fail.

The light strikes on the .357 SIG gun where off center. My first clue that the striker was being released before the trigger was pulled (I had another issue as well, that tied in and confused the problem). Someone here brought up the term "sear flutter". I understood that as the striker bouncing over the sear when the slide went forward.

I fixed that (so far) by stoning the surface of the APEX striker to make it flat, vs. the top of it being slightly tapered towards the front of the gun.

The second issue I had was a true light strike issue. Someone here mentioned "timing". I understood timing to be the issue of the striker block (APEX parts moved to the FS .357 SIG gun, from the 9MM) not being completely out of the way of the striker when the sear released it. I tweaked the hump on the back of the trigger bar that lifts the striker block upwards just a bit towards the rear and have been to the range 3 or 4 times now with a couple hundred rounds through the gun with the light strikers, failures to fire, etc. GONE. I'm still testing it before I clean it up for good and put it away in the safe for some future day.

Good luck with yours.
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Old March 21st, 2015, 06:52 PM   #6
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How exactly did you tweak the trigger bar? I may just put the factory striker block back in my 9c.
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Old September 10th, 2016, 06:21 PM   #7
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Location: SW Michigan
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I was having a similar problem with my M&P9. I measured the case length of the ammo. The ammo case length was out of spec. Try some different amo and see if you still have problems.
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