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Posted: 2/7/2015 3:22:15 PM EDT
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I recently completed the lower receiver of my AR15 build. To test that the lower receiver was functioning properly I put my Adams Arms upper on with no magazine. When I pulled the charging handle back the bolt carrier group locked in the buffer tube. I tried pushing the bolt catch button to release bolt carrier group but it did not come forward. So i'm trying to figure out if it's an incompatibility issue with AA upper or if it's a problem with the lower receiver.
Your thoughts would be much appreciated. Thanks! |
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Usually, a lower is function tested without an upper attached. Just simply cycle the safety on and off a couple times, then with your support hand thumb over the hammer, pull the trigger to feel the break. Your thumb prevents the hammer from slamming the wall of the mag well. With the trigger still held, push the hammer back down to assure the disconnector catches and finallymletmget of the trigger and it should click a third time as it resets.
Can you see what is hanging up? Possibly the disconnector didn't catch and the carrier is caught on the back side of the hammer? |
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Is there a spring and buffer installed inside the receiver extension ? This is the first thing I thought of when you said you charged it and the BCG didn't return to battery and got stuck inside the receiver extension. As already asked, is there a spring and buffer inside the tube? |
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The buffer sring came fully assemble and I just installed directly into the buttock of the gun. Here is a video that I put together showing the build of the lower. Let me know if you spot anything wrong.
[youtube]https://www.youtube.com/watch?v=j9UVaiZrImA[/youtube] Thanks |
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The buffer sring came fully assemble and I just installed directly into the buttock of the gun. Here is a video that I put together showing the build of the lower. Let me know if you spot anything wrong.  https://www.youtube.com/watch?v=j9UVaiZrImA
Thanks The video did not show anything regarding the build of the lower. |
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The video did not show anything regarding the build of the lower. Quoted:
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The buffer sring came fully assemble and I just installed directly into the buttock of the gun. Here is a video that I put together showing the build of the lower. Let me know if you spot anything wrong. https://www.youtube.com/watch?v=j9UVaiZrImA
Thanks The video did not show anything regarding the build of the lower. It at least cleared up the no buffer and spring theory. So far, that slightly higher bolt catch may be the issue. Did you peak around inside the ejection port, before splitting the halves, to see what was hanging up? Did it return to battery as soon as the receivers parted? |
| With the mag out and the charge handle pulled back the bolt catch does not work. With no mag the bolt catch only works if you set it manually. You should have function checked the lower/disconnector as detailed in the second reply, the BCG is probably hung up on the hammer. If you cannot get it apart try unscrewing the buffer tube being very careful with the fully compressed spring. |
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At 26 seconds into your video you had a hesitation with the buffer detent. Did it stick, as though the buffer was riding high over the detent ?
What happened here? ETA: take the buffer and spring out. Drop the bolt carrier into the extension. Does it slide freely ? Is the extension canted slightly off due to threading issues on the lower ? |
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I have not tried cycling the gun with the buffer spring out. I wondering now if the buffer tube is not correctly aligned with the lower receiver.
Here is another video I put together demonstrating the problem. Youtube Video |
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I have not tried cycling the gun with the buffer spring out. I wondering now if the buffer tube is not correctly aligned with the lower receiver. Here is another video I put together demonstrating the problem. Youtube Video Have you tried it with a different upper? |
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I would think that if the problem was a canted receiver extension/buffer tube, then the OP would feel the BCG dragging against the inside of the tube when he charges it since it would have to be canted pretty far off in order to actually hold the BCG in place just by interference fit.
OP, while the BCG is stuck in the tube, try holding your rifle vertically and lightly tapping the bottom of the stock on a hard surface, such as a concrete floor. Make sure to fully collapse your stock before doing this. I'm wondering if it is getting stuck because of a canted receiver extension if this jarring effect, or mortaring, would knock it loose and allow the stored tension in the spring to return the bolt to battery. If you try this, do it with the magazine removed so if it works the bolt will return all the way back to battery and not just slam into the bolt catch like it would if a mag were still inserted. |
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I have not tried cycling the gun with the buffer spring out. I wondering now if the buffer tube is not correctly aligned with the lower receiver. Here is another video I put together demonstrating the problem. Youtube Video Don't try cycling the rifle with no buffer and spring installed. This WILL result in the BCG getting stuck in the tube, as there will be nothing there to push it back into battery. If you wanna see if the tube is canted, simply remove your BCG from the upper and with the upper off of the lower and no spring or buffer installed inside of the tube, drop the BCG straight down into the tube and see if it moves back and forth freely inside, or if it binds and scrapes the inside of the tube. Keep in mind that only so much of the rear of the carrier will fit down into the tube before the gas key hits the top of the thread tower on the lower. |
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Don't try cycling the rifle with no buffer and spring installed. This WILL result in the BCG getting stuck in the tube, as there will be nothing there to push it back into battery. If you wanna see if the tube is canted, simply remove your BCG from the upper and with the upper off of the lower and no spring or buffer installed inside of the tube, drop the BCG straight down into the tube and see if it moves back and forth freely inside, or if it binds and scrapes the inside of the tube. Keep in mind that only so much of the rear of the carrier will fit down into the tube before the gas key hits the top of the thread tower on the lower. Quoted:
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I have not tried cycling the gun with the buffer spring out. I wondering now if the buffer tube is not correctly aligned with the lower receiver. Here is another video I put together demonstrating the problem. Youtube Video Don't try cycling the rifle with no buffer and spring installed. This WILL result in the BCG getting stuck in the tube, as there will be nothing there to push it back into battery. If you wanna see if the tube is canted, simply remove your BCG from the upper and with the upper off of the lower and no spring or buffer installed inside of the tube, drop the BCG straight down into the tube and see if it moves back and forth freely inside, or if it binds and scrapes the inside of the tube. Keep in mind that only so much of the rear of the carrier will fit down into the tube before the gas key hits the top of the thread tower on the lower. Wow, this is a great idea. |
| Update: So I took apart the buffer tube and re-installed the components. The bolt carrier group still was catching a little on the buffer tube. Here is what I did to fix that. With the upper and lower still attached I pulled the charging handle back- With the bolt carrier group back in the buffer tube I loosened the castle nut just little enough for the buffer tube to correctly align itself with the bolt carrier group. Not sure if this was safe/right thing to do.. but it seemed to fix my problem. Thanks for all the feedback guys! |
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Update: So I took apart the buffer tube and re-installed the components. The bolt carrier group still was catching a little on the buffer tube. Here is what I did to fix that. With the upper and lower still attached I pulled the charging handle back- With the bolt carrier group back in the buffer tube I loosened the castle nut just little enough for the buffer tube to correctly align itself with the bolt carrier group. Not sure if this was safe/right thing to do.. but it seemed to fix my problem. Thanks for all the feedback guys! This sounds as though the receiver is threaded slightly off its centerline. |
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Sounds to me like the receiver extension/buffer tube OR the lower receiver is poorly threaded.
When the receiver extension is threaded onto the lower receiver there should not be any play. Loosening the castle/locknut should not allow you to move the receiver extension around. Makes it sound like the something was incorrectly threaded. I'd try a different receiver extension/buffer tube to see if another one is also loose on the lower receiver. If it is, than I would suspect a problem with the lower receiver. If the 2nd receiver extension threads on more tightly, than I would suspect that your first/original receiver extension is defective/poor quality and in need of replacement. |
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