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Author Topic: Trigger systems and firing pins  (Read 1144 times)

Offline Lmbass14

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Trigger systems and firing pins
« on: May 02, 2015, 07:40:48 PM »
I have an AR 15 DPMS lower with a Stoner 7.62x39 barrel, bolt and bolt carrier group.  It came with a heavy duty Wolff trigger spring and the trigger pull was in access of 8# (highest my trigger pull gauge went), by a long margin.  It fired every round which is the good news.  The not so good news, is that with that trigger pull, it takes the fun out of it.

So I picked up Timney Trigger and  here are the results per box of 20 all FMJ except where noted.  This is all the different brands of ammo I have.  No problems with brass case.

Herters - 7 fail to fires

TCW (Tula Cartridge Works) - 8 fail to fires

MFS (Russian) - 0 fail to fires

Wolf Military Classic ( Hollow Point) - 13  fail to fires

Wolf Black Box (Hollow Points) - 13 fail to fire

Silver Bear - 5 fail to fire


That wasn't going to work, and thought, Wilson Combat would definitely work since the description says that it will fire all military surplus ammo.  Went to the Bullet Hole and ordered one (the M2 model).   

The install was a piece of cake  all of 30 seconds. It's real short take up before the wall, and a crisp break.  Did ten test pulls and all were 4 lbs.

Went to the range, and went through all the above boxes that wouldn't fire, and the Wilson Combat only fired 1 round of Wolf Black Box.  The rest of them went the dreaded "click".

My Brother suggested a modified firing pin and he just happen to have an extra pin that had .02 removed from the collar (don't know the correct nomenclature) and this is the result:

With Modified firing pin:

Tula - Perfect

Herters - Perfect

Golden Tiger - Perfect

Wolf Military Classic - Perfect

Silver Bear - Didn't use since I knew it would fire.

My question is: Is this normal to have to use a different firing pin along with the trigger group?  I was ASSUMING that the WC trigger would have a strong enough spring to ignite all the ammo.  Yes I know the Russian ammo is notorious on having deep set primers and that is the culprit and all the primers strikes looked normal.

I did contact WC customer support, and they sent me a replacement trigger group, but had the same result, and at this time the engineers "are looking into it".  Yeah right.

Your thoughts are appreciated.

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Offline RobertH

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Re: Trigger systems and firing pins
« Reply #1 on: May 02, 2015, 07:57:28 PM »
i'll be following this thread....
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Offline shooter

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Re: Trigger systems and firing pins
« Reply #2 on: May 02, 2015, 08:07:20 PM »
 SO, you have a extra timney trigger?  talk to me about it!


  sounds like the firing pin tip was to short. if adjusting the length a little and it works, I wouldn't worry about it
« Last Edit: May 02, 2015, 08:24:00 PM by shooter »
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Offline tstuart34

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Re: Trigger systems and firing pins
« Reply #3 on: May 02, 2015, 08:35:39 PM »
Just curious have you tried a different bolt? Maybe it's not the firing pin.

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Offline Lmbass14

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Re: Trigger systems and firing pins
« Reply #4 on: May 02, 2015, 08:36:29 PM »
shooter, gave the Timney to my Brother. 
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Offline Dan W

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Re: Trigger systems and firing pins
« Reply #5 on: May 02, 2015, 09:05:42 PM »
Never heard of this before. Can you be more specific about the modified firing pin?

Where was the collar shortened and how far does it protrude from the bolt face when the bolt is in firing position in the carrier?

Compare that to the original firing pin's protrusion.

If the firing pin sticks out too far, there is a possibility that it might be able to fire out of battery or even slam fire
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Offline RobertH

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Re: Trigger systems and firing pins
« Reply #6 on: May 02, 2015, 09:31:14 PM »
just a question... is the firing pin an 7.62x39 or a standard ar15 firing pin?
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Offline Lmbass14

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Re: Trigger systems and firing pins
« Reply #7 on: May 03, 2015, 07:04:34 AM »
Really good questions.

Bob - If the firing pin was too short, why did it work with the Wolff spring?  Originally that told me it wasn't the firing pin.

tst - Great thought and no, didn't try (and don't have) an extra bolt.  And to be honest, didn't think the bolt could be the issue. The head space was tested, and it was a go. 

Dan - Now you going to make me find the calipers that was put in a "safe" place.  I'll have to get back with you on that one.  You did bring up a good point about slam firing.  Didn't test the modified pin with brass ammo.  Need to do that.

Robert - The original one was 7.62 firing pin, going to ask my Brother on the modified one.
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Offline shooter

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Re: Trigger systems and firing pins
« Reply #8 on: May 03, 2015, 01:00:27 PM »
 maybe the wolf spring hit the firing pin hard enough to fire the shell. by bouncing the firing pin,  how big of a dent were in the cases that didn't fire?

  and a second question, why did you try to make a AR-15 fire 7.62-39? there are already a load or AK,s out there that fire that case with no problem?

   and will I be taking the rifle to the gun shows in the fall?
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Offline Lmbass14

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Re: Trigger systems and firing pins
« Reply #9 on: May 04, 2015, 03:18:50 PM »
Since Dan force me to find the calipers since the move, guess this needs to be updated.

The original fp is 3.185" and the modified one is 3.225".  Couldn't get the calipers to get an accurate measure on the protrusion of the fp, so had a sharpie and marked it, then measured the mark.  And that measurement of the original was .041 and the modified was .043

Here are some pics showing dimple and primer depth.

Golden Tiger



Wolf



Herters



Tula



Bob -  will keep this one, might give you a M44 to sell though.
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Offline Dan W

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Re: Trigger systems and firing pins
« Reply #10 on: May 04, 2015, 06:47:29 PM »
Quote from: Lmbass14 on May 04, 2015, 03:18:50 PM
The original fp is 3.185" and the modified one is 3.225"

.040" is quite a bit and likely your culprit
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