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Centerfire Rifles - Semiautomatic or Gas Operated Centerfire rifles, carbines and other gas operated rifles.

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  #1  
Old 05-20-2013, 6:01 PM
AUstate AUstate is offline
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Default Anybody ever have their AR-15 hammer pin break?

I know this is the Centerfire forum, but since the problem is on a AR-15 Lower I think it is pertinent here.

I was having tons of light primer strikes on a CMMG complete .22lr upper that I could not diagnose at the range.

Tried cleaning, relubing, field stripping, and even removing firing pin to check for debris.


It was not untill I got home and started completely taking apart my lower to clean more thoroughly I noticed the hammer pin was not sitting flush on one side. It was sticking out just a little bit...
I then looked at the other side and it was also sticking up there as well.... for a good 7 seconds I was very confused and thought maybe I had installed the wrong pin.

So when I carefully pushed out the pin it was obviously in 2 pieces. A very clean break right in the middle. So clean it is almost hard to tell its a break.

The LPK came from a local Gunstore. I have their LPKs in 2 more 5.56 AR builds and have not had any issues.


This lower and LPK have only been used on a Complete CMMG .22lr Upper.

And I would venture to guess I have probably put a little over 3000 rounds through it. Never had any problems at all to speak of until the last 2 or 3 range trips. Just kept getting so many light primer hits. I imagine this pin is the culprit, and it must flex a little and give enough to slow the hammer down from a good solid hit.

So thought I would share my story. I have never really heard of hammer pins breaking, but I admit I have never searched it out yet.

Also Im curious to what you guys think. Is this most likely a freak manufacturing problem. I have spent lots of time trying to see if someting on the hammer is helping to wear or cause problems, but everything looks good.

And with the way the break looks, it doesnt show anywear. Just a super clean break.






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Old 05-20-2013, 6:08 PM
tal3nt tal3nt is offline
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I've read of it happening to someone here before not too long ago. Do you know the manufacturer of the parts kit? After taking a long look, that center groove on the pin does appear to be an inherently weak point of the pin tho. I would just replace it and not worry too much
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Old 05-20-2013, 6:11 PM
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Jeymz Jeymz is offline
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That's a first for me. Never seen that happen. Check out KNS anti rotation pins. Solid all the way through with no grooves.
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Old 05-20-2013, 6:19 PM
tal3nt tal3nt is offline
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FWIW The kit that I read on was a DPMS. Broke just like yours
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Old 05-20-2013, 6:21 PM
AUstate AUstate is offline
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Quote:
Originally Posted by Jeymz View Post
That's a first for me. Never seen that happen. Check out KNS anti rotation pins. Solid all the way through with no grooves.
Its pretty funny, I was always the guy who would say something like that is totally not necessary. Pretty sure I can remember telling a friend theres no point for using KNS pins....

Pretty crazy, and to happen on a relatively low round count too.

I do not know the actual manufacture of the LPK, but I will have to bring it in and show the Gunshop who sold it.
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Old 05-20-2013, 6:24 PM
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Quote:
Originally Posted by tal3nt View Post
FWIW The kit that I read on was a DPMS. Broke just like yours

When I find out who was the manufacture of the kit I will have to remember and update the post.
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  #7  
Old 05-20-2013, 10:40 PM
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I recently noticed my hammer pin was broken.
It was a dpms lpk.
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Old 05-20-2013, 10:41 PM
gregshin gregshin is offline
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Had a rock river arms break on my 9mm build. Replaced with kns pins
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Old 05-20-2013, 10:43 PM
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Blowback guns eat hammer pins because the hammer is directly taking the force of the bolt coming back when the bolt opens.
In a locked-breach AR, the high pressure spike is gone before the carrier is opened by gas.
On the blowback design, the full pressure of firing forces directly back against the hammer and hammer pin.

The solid KNS pins or the JP pins with clips on the outside are the best solutions for blowback operated lowers.
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  #10  
Old 05-21-2013, 8:54 AM
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I had the hammer pin break while shooting a older high round round CAR15, takes the gun right out of action.

KNS pins are many times more durable than GI spec pins, if your worried about it in the future get some.
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Old 05-21-2013, 10:57 AM
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DPMS
Attached Images
File Type: jpg 2012-02-16_19-21-48_904.jpg (71.7 KB, 53 views)
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  #12  
Old 05-21-2013, 11:19 AM
jchen76@gmail.com jchen76@gmail.com is offline
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Happened to me, using CMMG parts kit on spikes tactical lower. Used the lower for about 3k of shooting using dedicated 22lr upper. Switched to 5.56 upper and after 200 rounds, pin snapped in two like your pic.

I've read it's very common issue to 22lr conversion/dedicated upper to have this happen.
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Old 05-21-2013, 10:46 PM
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Had this happen last year with a DPMS LPK. ~4k centerfire through it, and about the same with a .22 conversion.
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Old 05-21-2013, 11:52 PM
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Never had that problem because all my ARs get KNS pins.
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Old 05-25-2013, 12:07 AM
AUstate AUstate is offline
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Thanks for all the info everyone.

Ordered some KNS pins from good ole Joe Bobs.

I got a email saying they were shipped 3 hours after ordering!

Pretty good price too,

http://www.joeboboutfitters.com/KNS_...kns-replth.htm
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Old 05-25-2013, 12:19 AM
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While I'm sure blowback doesent help, I'm wouldn't exculpate dpms in the matter. I've used a lot of their lower kits over the years, despite all the horror stories worst case was sometimes some of the roll pins were a tad oversized, but no biggy. But recently my buddy got one with an out of spec hammer, so that's it for me, no more cheapo dpms kits
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Old 05-25-2013, 9:53 PM
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Quote:
Originally Posted by ar15barrels View Post
Blowback guns eat hammer pins because the hammer is directly taking the force of the bolt coming back when the bolt opens.
In a locked-breach AR, the high pressure spike is gone before the carrier is opened by gas.
On the blowback design, the full pressure of firing forces directly back against the hammer and hammer pin.

The solid KNS pins or the JP pins with clips on the outside are the best solutions for blowback operated lowers.
^^^This

A lot of the people I know who had this happen to them was because they shot about 10,000 rounds full auto . They always complained about their pins snapping.
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