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Centerfire Rifles - Semiautomatic or Gas Operated Centerfire rifles, carbines and other gas operated rifles.

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  #1  
Old 10-17-2018, 4:14 PM
MajorCaliber MajorCaliber is offline
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Default BCG getting stuck back in buffer tube

A friend and I are building ARs from 80% lowers with the same jig and tooling but starting with different MFGR blanks. Mine works just fine when paired with my Aero Precision upper and high end Sharps balanced BCG. When my upper and BCG was paired with friends lower with no mag in place, the charging handle was very stiff to pull back and BCG stuck in full rear position. It stuck about a behind contacting the bolt catch and bolt catch moved freely with no effect. I was able to CAREFULLY pry the bolt forward using a wooden chopstick. I replaced my BCG with a MilSpec BCG and charging was stiff but the BCG would return forward. Either of the BCGs will work with my upper and lower. I dont have a second upper to try at this moment. The problem is not related to the buffer or spring because interchanging the buffer and springs had no effect in either lower, and when both buffers are depressed manually in their respective lowers with a wooden dowel, they depress to the same depth and return freely.

Any idea what the cause of problem is?
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  #2  
Old 10-17-2018, 5:10 PM
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Sounds like an out of spec lower.

Check to make sure his rear pocket is milled out enough
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  #3  
Old 10-17-2018, 5:19 PM
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Look for wear marks.

Also check to make sure the buffer tube hole in the lower is drilled at the correct height and straight.
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  #4  
Old 10-18-2018, 7:03 AM
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I once had a similar issue. In my case it was a result of the front of the pocket in the receiver needing a slight bit of material removed. As it was the hammer was binding on the front pocket, and that was causing the bolt to bind on the hammer.
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  #5  
Old 10-18-2018, 7:57 AM
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sometimes it isn't the BCG in the buffer tube.

Check that the castle nut and butt plate dont stick too high above the buffer tower.

You can see that the charging handle can get stuck and will leave aluminum shavings on the top of that area or witness marks that show the charging handle is contacting the buttplate or castle nut and will cause enough friction for none of that stuff to move freely.

if thats the case you'll need to file down till everything clears. this happens on mil spec rifles as well.
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  #6  
Old 10-18-2018, 4:43 PM
MajorCaliber MajorCaliber is offline
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Thanks for all the advice. I'll probably never get to the bottom of this, because once we had the friend's completed upper in hand, it mated to the lower and functioned flawlessly, so neither of us were inclined to spend time playing Sherlock Holmes, and certainly not to make any modifications that were at that point completely unnecessary.
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  #7  
Old 10-18-2018, 4:50 PM
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sometimes, having the gun fully together will solve fitment issues that half completed parts display.
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  #8  
Old 10-18-2018, 4:50 PM
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Sounds like CHEAP A** PARTS.
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  #9  
Old 10-18-2018, 4:53 PM
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Nope he even specified “high end”
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  #10  
Old 10-18-2018, 7:31 PM
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Check to make sure your buffer tube is installed correctly and that the buffer detents are captured properly by the buffer tube. The BCG's path is clearly being obstructed by something.
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  #11  
Old 10-19-2018, 1:10 AM
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Still sounds like an issue with doing 80% builds....

My 80% function checks fine, but sure isn't the same as my aero m4e1 or spike's
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  #12  
Old 10-19-2018, 12:47 PM
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Just to clarify, Yes, I would call the upper "high end" or at least not "cheap A**" with the relevant parts being an Aero Precision enhanced upper and Sharps balanced BCG with DLC coating. The charging handle was standard, and I can't imagine the other upper parts such as barrel or handguard could be relevant. The lower was build from an 80% lower, PSA lower parts kit, buffer tube, buffer and spring from Thorsden. I did check the buffer retainer and it was properly captured at the shoulder and functioning properly. I also did check the alignment of the buffer tube to the lower, and lacking sophisticated measuring gear, it was straight in both dimensions within what my eyeballs can detect, and the buffer and spring moved freely in the buffer tube throughout its travel when pushed by a dowel.
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Old 10-19-2018, 1:41 PM
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A nice heads up post. Thanks. Note to self...must add chopsticks to range bag...
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Old 10-19-2018, 2:05 PM
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Good luck. Let us know what the issue is once its resolved(with pictures please).
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  #15  
Old 10-19-2018, 4:32 PM
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Quote:
Originally Posted by MajorCaliber View Post
Just to clarify, Yes, I would call the upper "high end" or at least not "cheap A**" with the relevant parts being an Aero Precision enhanced upper and Sharps balanced BCG with DLC coating. The charging handle was standard, and I can't imagine the other upper parts such as barrel or handguard could be relevant. The lower was build from an 80% lower, PSA lower parts kit, buffer tube, buffer and spring from Thorsden. I did check the buffer retainer and it was properly captured at the shoulder and functioning properly. I also did check the alignment of the buffer tube to the lower, and lacking sophisticated measuring gear, it was straight in both dimensions within what my eyeballs can detect, and the buffer and spring moved freely in the buffer tube throughout its travel when pushed by a dowel.
I mention to check the butt plate and castle nut in post #5. Did you report back on that?
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  #16  
Old 10-19-2018, 6:39 PM
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Check the bolt carrier in the upper by itself, it should slide smooth. Some upper receivers have been known to be tight. Try cleaning the bolt carrier group, the upper, lube it up and try it. Chances are that the upper receiver is out of spec. But try the bolt carrier by itself and it should slide nice n easy if it binds just a little, with spring pressure, up, down, left or right, it would be worse.
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  #17  
Old 10-21-2018, 10:03 PM
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Quote:
Originally Posted by jameshenry View Post
A nice heads up post. Thanks. Note to self...must add chopsticks to range bag...
My gunsmithing tool kit contains a number of wooden chopstics and similar wooden implements that I use whenever prying or having to apply more than fingertip force to gun parts and their finishes. Wood is soft enough not to scratch or deform any of the metal on a gun.
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  #18  
Old 10-21-2018, 10:09 PM
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In response to the latest questions, the BCG was fine in the upper and in the buffer tube without the spring. Yes, I checked the castle nut and the end plate and they were fine.
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  #19  
Old 10-22-2018, 8:03 AM
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This may be way off track, but I had a problem once with an old Colt and mismatching upper. Mismatching lots of parts actually. The BCG seemed to get stuck in buffer tube. So I thought. Turned out to be the BCG dragging badly on the hammer.

So this may be a wrong-tree bark-up, but maybe try removing your hammer and see if the BCG cycles correctly?
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