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Old 05-27-2013, 07:59 AM   #1
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Default AR Build - 1st shot problem

I built a new AR using a PSA lower, PSA LPK, and an upper custom built by a friend who is a Class III manufacturer. It has a chromed bolt of unknown origin, but appears extremely high quality.

After assembly, I tend to run the gun a little on the wet side of normal for the first few hundred rounds to make sure nothing is damaged getting broken in. However, for the first time in several builds, this gun fired one round, unlocked out of battery, but the bolt only recoiled a very minor amount, maybe a quarter of an inch. A few taps with a punch and gunsmithing hammer backed the bolt out and extracted the round. Inspection shows nothing broken or galled, so I'm not sure what happened. Has anyone else experienced a condition like this before? If so, what did you do? I know a gunsmith should inspect it but I wanted to find out the cause first, if possible.



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Old 05-27-2013, 01:44 PM   #2
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Does the BCG cycle smoothly by hand? If excessive friction isn't noticed, and assuming good ammo, then maybe a gas leak...

How did the brass and primer look?



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Old 05-27-2013, 04:56 PM   #3
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Yes, had a similar problem when a bolt on gas block was installed all the way up against the ridge on the barrel, aft of the block. It partly blocked the gas port, causing a under gassing problem, resulting in short stroking.

Also saw it on a rifle, where the gas tube retaining pin walked out and the gas tube was floating, causing the gas port to get blocked.

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Old 05-27-2013, 05:01 PM   #4
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Not a "gas" issue if he had to use a hammer and punch to get the BCG back, right? I'd focus on the BCG, surrounding parts, and receiver.

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Old 05-27-2013, 06:27 PM   #5
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I would check the inside of the upper and see where the BCG was rubbing. if you have ANY damage to the upper I would get the gun to a smith asap. It could be something as simple as lubing the wrong areas or something as bad as the BCG being out of spec in its machining.

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Old 05-28-2013, 12:03 AM   #6
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Try a different BCG in your rifle and see what happens if indeed the bcg was truly stuck. Alternatively you may try your new bcg in another AR. That'll tell you if the upper or BCG are out of spec. Somestimes there is such a thing as tolerance stack. One part +.002, one part -.002 give you a .004 difference. Doesn't seem like alot, but enough to cause failure.

If the new BCG causes problems something may be wrong with your upper receiver. The reason it's probably not a gas issue is because you had to tap back your bcg. Does the bcg move freely with the charging handle? You may still want to check the gas system. I usually do this by plugging the barrel extension with some cotton and blowing in the barrel. I do this while the gas block is loose and wiggle the gas block listen for differences in the pitch and tone of the whiste of the blown air.

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Old 05-28-2013, 02:35 AM   #7
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Quote:
Originally Posted by Quentin
Does the BCG cycle smoothly by hand? If excessive friction isn't noticed, and assuming good ammo, then maybe a gas leak...

How did the brass and primer look?
Primer and brass were normal, but it seemed like the brass was holding the bolt closed. After extracting case, bolt seemed to cycle fine.
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Old 05-28-2013, 02:38 AM   #8
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Quote:
Originally Posted by HockaLouis
Not a "gas" issue if he had to use a hammer and punch to get the BCG back, right? I'd focus on the BCG, surrounding parts, and receiver.
Seemed that the brass was what was locking up because there wasn't any resistance with light blows, i.e. didn't have to break it free, but resistance seemed to be in the chamber.
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Old 05-28-2013, 02:47 AM   #9
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CGS, I will try new BCG as I have a couple if M-16s that just arrived that will be a good choice. I love the idea of checking the gas block and tube so will try that, too.

Upper receiver didn't have any rub mark or gouge and BCG moved freely with charging handle when brass was extracted. I am going to disassemble, re-inspect, re-lube and test fire. I'll post here as soon as I can get to the range.

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Old 05-28-2013, 02:50 AM   #10
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You said it was a custom built upper? Let your friend look it over, he will be the most familiar with it.



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