Old 04-21-2008, 13:01   #1
ODA 226
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CAR-15 Problems

I'm an SF Weapons man, but need a second opinion before I proceed further...

I built a CAR-15 from an NFA lower. M-4 flattop, quad rail, 11.5" barrel, pneumatic buffer.

The weapon function flawlessly in semi-auto, but when I flip it to full-auto, I get 3-4 rounds then a light primer strike resulting in a failure to fire. This only happens on full auto. Never encountered this type of problem before...

I'm thinking weak hammer spring or firing pin. Any other ideas?

226
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Old 04-21-2008, 13:54   #2
JJ_BPK
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Quote:
Originally Posted by ODA 226 View Post
CAR-15 from an NFA lower. M-4 flattop, quad rail, 11.5" barrel, pneumatic buffer.

I'm thinking weak hammer spring or firing pin. Any other ideas?

226
If that doesn't fix the problem,,

1)swap out the buffer
2)check alignment of upper & lower & buffer
3)lap the bolt/carrier/upper for a couple hundred rounds

Also if the gas port position or barrel length was altered, the gas port size may need to be altered to account for the timing pulse..

ref:

http://www.armalite.no/downloads/Tec...,%20030824.pdf

Good Luck..
Jim
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Old 04-21-2008, 14:13   #3
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Sounds like the weapon is out of time.

Before I did anything else, I would pop in a 2xH or 3xH buffer and see if that fixed it.

Then consider the other dynamics of the timing.

Best of luck!

TR
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Old 04-22-2008, 09:00   #4
ODA 226
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Roger that fellas. When I return from Germany, I'll go through your suggestions step-by-step. Thanks!

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Old 04-22-2008, 16:07   #5
BryanK
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Quote:
I'm thinking weak hammer spring or firing pin. Any other ideas?

Without being able to see the rifle first hand, or knowing the manufacturer(s) of each part, It could be the gas tube, or like you stated, the firing pin. Is the hammer spring seated correctly? Brownell's sells a pigtail tube that may correct the deficiency. Here is the site with a description of what it does.
http://www.brownells.com/aspx/NS/sto...GTAIL+GAS+TUBE Hope it provides an option for you.
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Old 04-22-2008, 16:14   #6
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Could it be weak Sear and/or Disconnect Spring(s) allowing the hammer to follow the bolt occasionally??
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