bcg too tight in the upper?

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[ARCHIVED THREAD] - bcg too tight in the upper?

Posted: 2/7/2006 9:54:27 AM EDT

I took my new AR to the range yesterday to sight it in and I ran into a problem. The bcg is way too tight in the upper. With the bolt installed, the carrier won't move freely in the upper. I tried a different bcg in my upper and it was fine, and tried my bcg in another upper and it was too tight. But without the bolt, the carrier drops right in. I even tried a different cam pin in my bcg and it didn't make any difference.

The upper is an LMT and the bcg is a new Stag/CMT. I was planning to e-mail Stag, but I thought I might ask here first and see if this is something easily fixable, or a common problem.

Anyone?

Posted: 2/7/2006 10:48:19 AM EDT

[#1]

Quoted:

..... With the bolt installed, the carrier won't move freely in the upper.....

.....But without the bolt, the carrier drops right in......

That's pretty odd. Is it possible that the bolt carrier has a crack in it (maybe on the bottom side), and thus installing the bolt causes the carrier to expand outward?

Posted: 2/7/2006 10:54:41 AM EDT

[#2]

And how was it AFTER you shot it?

Loosen up any?

Mike

Posted: 2/7/2006 11:00:10 AM EDT

[#3]

Take the gun apart, put the bcg in the upper with and without bolt, and try to get a better look at where it's snagging.

Posted: 2/7/2006 11:18:01 AM EDT

[#4]

Quoted:
And how was it AFTER you shot it?

Loosen up any?

Mike

Well, I only shot it maybe 8-10 times, because it was too tight to cycle.

Posted: 2/7/2006 11:55:35 AM EDT

[#5]

Life made simple.

Pull cam from working B/C and install it in non-working B/C. If the cam swap isolates the problem to the new cam being the problem, then you need a new cam for the new LMT tighter upper track.

If the old cam in the new B/C is still binding in the upper, take a straight edge and see if the sides of the key and the sides of the cam line up with the bolt in the forward unlocked position. Here, it's going to come down to either the carrier slot not being milled correctly/bur'd (allowing the bolt to fully cam forward) or you have a defective key (sides not parallel with the screw center line) that is causing the problem.

Posted: 2/7/2006 12:34:09 PM EDT

[#6]

Quoted:
Life made simple.

Pull cam from working B/C and install it in non-working B/C. If the cam swap isolates the problem to the new cam being the problem, then you need a new cam for the new LMT tighter upper track.

If the old cam in the new B/C is still binding in the upper, take a straight edge and see if the sides of the key and the sides of the cam line up with the bolt in the forward unlocked position. Here, it's going to come down to either the carrier slot not being milled correctly/bur'd (allowing the bolt to fully cam forward) or you have a defective key (sides not parallel with the screw center line) that is causing the problem.

I'll check that out. I tried someone elses's cam pin in my BCG and it was the same, so it's probably one of the two second issues you mentioned.

Posted: 2/7/2006 5:24:51 PM EDT

[#7]

Double check that the firing pin retaining pin is fully seated below its recess, and does not extend past the other side of the carrier. The pin MUST be inserted (bolt facing forward)left to right.

[ARCHIVED THREAD] - bcg too tight in the upper?

AR-15 » Troubleshooting

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