9MM Ar Double Tapping

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9MM Ar Double Tapping

Postby stratusww » Sat Jun 25, 2011 4:40 pm

:bang: Hi everyone, sorry to resurrect this zombie post, but I at least have more info and photos this time. So far, not much luck in getting answers from the Oly channel, but I am reading more and more in other forums that seem to be similar to my issue. Any one else experiencing this as well since my last thread here: viewtopic.php?f=65&t=11810&start=25

Anyhow, I have more info and photos, along with better description if anyone has any thoughts. Thank you in advance,..... Here goes:

Problem:
• Irregular action from 2 clone 9mm AR carbines. Misfeeds, Double-tapping and occasionally the bolt doesnt ride forward far enough when charging. Double/triple tapping is more common than jams.


Learnings and Findings:

• Seemingly, automatic fire is Not caused by lubricant on the fire control group, or excessive dirt build up.
• All Lowers work perfectly when firing .223 rounds, failures only happen with 9mm


Carbine #1 Specs:
• Olympic Arms Upper
• DPMS Lower 5.56
• Magpul Mil-spec CTR stock
• DPMS Lower Parts Kit (5.56)
• Milspec buffer spring

Carbine #2 Specs:
• Olympic Arms Upper
• DPMS Lower 5.56
• Magpul Mil-spec ACS stock
• DPMS Lower Parts Kit (5.56)
• Milspec buffer spring

Ammo Used:
• Various 124 Gr ammo (Winchester, Magtech)


Recent Range Trip Notes:
I took 3 Olympic Polymer 9mm magazines, 2 of which were brand new and never used. Double-tapping might be anywhere from 2-3 shots at a time with one trigger pull. Misfeeds are often characterized by a round getting crushed between the bolt group and the previous round or the rim of the barrel.

1. Brand New mag. 10 shots. 3 misfeeds.
2. Brand New mag. 10 shots. 3 misfeeds. 1 double tap
3. Old mag. 10 shots. 2 double taps.
4. Brand New mag 10 shots. 1 double tap. 2 misfeeds.
5. Brand New mag. 10 shots. 2 double taps.
6. Used mag. 10 shots. 2 double taps. 1 misfeed

6-25-11
3rd lower brought in to experiment, still double/triple taps.


Thoughts

My latest thought is that the hammer is bouncing off the disconnector tail. Rather than being caught, it bounces back and forth a few times sending a round out as it does. Is that possible? Would a different hammer be a better choice than the standard one i am using for these?
1.jpg
2.jpg



Here is a function test I just shot a video for.
(I know what you are thinking and that is not my chihuahua.)



Possibly a Similar Issue?
http://boardreader.com/thread/9mm_AR_double_tapping_15h3X2nc3.html

http://www.ak47.net/archive/topic.html? ... 5&t=188319

http://www.ar15.com/forums/topic.html?b=3&f=15&t=140693
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Re: 9MM Ar Double Tapping

Postby 9x19MdM » Sun Jun 26, 2011 6:29 am

Dry firing like that in the vid can cause the bolt catch to break.
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Re: 9MM Ar Double Tapping

Postby John A. » Sun Jun 26, 2011 6:51 am

Is it an olympic built 9mm?

Is the fire controls built by olympic?

If the answer to both is yes, call them and send it back to them for repair. Let them deal with it.
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Re: 9MM Ar Double Tapping

Postby Globemaster » Sun Jun 26, 2011 7:17 am

agreed ...
The Nonsense Stops! … When The Hammer Drops!
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Re: 9MM Ar Double Tapping

Postby stratusww » Sat Jul 16, 2011 5:25 pm

Good news. I spoke with Andy this week and he gave me some instructions on how to Dremel out the front of the Disconnector. I tried it on one of my Carbines, took it to the range and so far so good! I posted a picture for the few people like me who had little idea what this piece was without googling it. One more rifle to fix and I'll report back if that one works as well.
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Re: 9MM Ar Double Tapping

Postby Rattler » Sun Jul 17, 2011 4:08 pm

stratusww wrote:Good news. I spoke with Andy this week and he gave me some instructions on how to Dremel out the front of the Disconnector. I tried it on one of my Carbines, took it to the range and so far so good! I posted a picture for the few people like me who had little idea what this piece was without googling it. One more rifle to fix and I'll report back if that one works as well.


Relieving the under side of the leading edge of the disconnector, allows the disconnector to rock forward further to get a better purchase on the disconnector sear of the back of the hammer. This prevents "following" m where the hammer follows the bolt carrier forward and the impact (due to the blowback system) can sometimes be enough to set off the next round. Adding more area of purchase for the disconnector to the hammer prevents this hammer disconnector "miss" as they pass by one another. Too much puchase surface area, and the two do not disconnect, and the disconnector will not release the hammer at all.
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