AR-15 Failure to Feed

Shawnyc

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So I have over one thousand rounds through my AR (10.5” SBR). I am now getting pretty frequent FTF where the round is jammed between the bottom of the bolt and the feed ramp. Also, the bolt doesn’t hold open on the last round.

Unfortunately I have changed two things simultaneously and I don’t know which one is the issue. I ran over one hundred rounds of 22lr through it using the CMMG conversion the last time out, and I installed a new Fail Zero nickel boron BCG.

At this time does it sound like the 22lr ammo gunked up the gas system causing the BCG to short stroke? Or is there an issue with the Fail Zero BCG.

I’m going to try to get to the range again tomorrow and run it with a milspec BCG.

EDIT: This occurs with multiple types of magazines.
 
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citoriguy

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I'd start with the BCG too. I have a couple FailZeroes and haven't had an issue, but many have had them of one kind or another.
 

92G

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return to original BCG
fire with 1 round in mag
if fail to lock open, its undergassed
most common cause for this is gas block has shifted such that has tube no longer in alignment with port. I’m putting my money on this. I have had this happen. It’s common for those who actually shoot their rifle (as you’re doing).
 

SJan

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100 rounds of even the dirtiest 22 shouldn't be enough to gum up the gas port/gas tube. Even so, it is recommended to thoroughly clean after using a 22 conversion.

In your case it's probably the BCG that you changed. Other less likely cause is something worked loose in the gas block area. Is it a pinned block? Or a set screw style?
 
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Uzi2

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The CMMG kit has a block between the 22lr bolt and buffer. Essentially the buffer tube doesn’t get used.
The GAS TUBE still gets shit in it from the .22 going down the barrel.

Flatten the end of a piece of 16ga steel wire and "roto root" the gas tube then run some .223 ammo through the gun.

Then check for gas key leakage on your new bolt carrier and run the rifle wet.
 

Uzi2

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The buffer tube the same for 22 lr and 556 ?
.22LR conversions are blowback operated, directly from their own chamber using their own small buffer spring.

They can foul a gas tube with unburned powder and lead as the bullet passes by the gas hole in the barrel.

The buffer tube is on the rear of the rifle.:)
 
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I would say unless you shot thousands of rounds of 22lr the gas tube is not blocked. Unless your gas port is shaving lead of the bullet.?
 

Uzi2

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I would say unless you shot thousands of rounds of 22lr the gas tube is not blocked. Unless your gas port is shaving lead of the bullet.?
By making a couple of hundred ( not thousands) lead shavings that would fit through a gas hole's diameter, I think you'd be surprised at the volume.
 
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By making a couple of hundred ( not thousands) lead shavings that would fit through a gas hole's diameter, I think you'd be surprised at the volume.
I put a cmmg insert on my stag during the ammo shortage. I burned up my oldest 22lr in the hoard. Aprox 3500 rounds. Never cleaned it ran fine.
Now a friend brought me his ar after 500 rounds and I plucked a chunk of lead out of the front sight port? I also have ran cast 224 bullets through my AR with zero issues.

Its all fun ,
 

Shawnyc

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Partial update. Couldn’t get to the range. Stripped and cleaned the gun, lubed it up good. Hand cycled mags of five snap caps. First mag hung up once. Hand cycled about twenty more mags of five snap caps with no issue. Now I’m thinking she was just dirty but a range test is coming this week.
 
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