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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/02/2014 at 22:31
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I just assembled a new AR15 upper that is a really nice single shot at the moment. The round chambers fine, seats and fires but the it will not eject. I didn't think to check to see if the BCG would lock back after firing one round, but I don't think it's moving far enought to eject the round anyway. So my guess is that it is under gassed at the moment, but not for sure. Ammo was Federal 55 grain 5.56mm XM193 Ball. I also didn't think to try the Winchester 55 grain white box I had with me, to see if that made a differance. I was also using a Pmag.
 
Here are the components:
 
Seekins forged upper
Rainier 18" SPR contour barrel, with rifle length gas system
YHM low profile gas block
WOA rifle length gas tube
Spikes tactical full auto BCG
15" MI Quad Rail
YHM 5M1 compensator
 
Seekins forged lower
CMMG lpk
Magpul CTR stock kit with carbine buffer
 
Here's my thoughts so far. First I need to double check to make sure the gas tube is clear and the ports are lined up. I am certain that the gas tube hole in the barrel nut is perfectly centered on the upper. Beyond that, I'm not sure where to start. My other guess is that maybe the spring and buffer aren't matched to the rifle length system. I did swap BCG's and the rifle did the same thing with the generic PSA BCG as well.
 
Any thoughts. Thanks for the help.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/03/2014 at 05:29
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Is the gas key loose/staked?  
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/03/2014 at 07:08
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Also, make sure the port in the gas block is aligned with the gas port on the barrel, and that both aren't obstructed.

Edit: ...but I believe you mentioned that already.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/03/2014 at 08:32
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Both Ted and Mark offer great suggestions.  Also look for any fouling leaking around the gas block, would indicate a loose gas block.

I have had this happen on one occasion with an upper that I helped someone assemble.  Once he got it home it would fire one round, eject and that is it.  I tore the upper down, checked the size of the gas port, it was fine (0.093-0.096), gas tube was not blocked and everything was lined up.  What I did notice was that the bolt, bolt carrier and upper receiver were bone dry.  I lubed it up and test fired it and it functioned properly.  My buddy wasn't applying enough lube. 

I don't know how much lube you put on, but I run my new builds pretty wet until the get broken in a little.



Edited by cpwomack - July/04/2014 at 13:32
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/03/2014 at 09:13
mil169 View Drop Down
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I'm fairly sure the bcg isn't the problem, simply because I tried a differant one that works in my 16" middy. But I will look that over as well. The upper was pretty wet as well, I thought I may have over oiled it. Unfotunatley I can't mess with it again until next  week. But when I can, I will remove the gas tube and block and blow air through everything to make sure it's clear. The barrel has the set screw dimple and I used the YHM set screw low profile block, so I don't think I could have messed that up, but I will check.
 
Any thoughts on the buffer and spring being mismatched to the rifle length gas system.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/03/2014 at 09:29
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You should not have a problem running a carbine buffer and spring with rifle length gas, I have done it in the past and never had any problems.  Not all gas block are the same dimensions, so the screw dimple may be set-up for a different gas block.  I doubt that is the problem, but it is worth checking, the hole in most gas blocks is oversized.

Start at the gas port and work your way back:

Check the size of the gas port.

Measure the distance from the edge of the gas block to the gas port in the gas block.  Use this measurement to determine if the dimple works with the YHM gas block.

Check the gas tube to make sure it is not blocked.

Check the torque on the gas keys.

If none of that helps, then I am out of ideas.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/03/2014 at 09:31
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Also do quick inspection of bolt to make sure it is not installed backwards, an assembly problem I once experienced when Robar returned a newly NP3 plated BCG for my 6.5 Grendel with the bolt installed 180 degrees backwards so the extractor was in the 9:00 position rather than 3:00.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/03/2014 at 09:45
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I didn't see the part where you tried a different bcg.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/03/2014 at 09:49
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Originally posted by Rainman Rainman wrote:

Also do quick inspection of bolt to make sure it is not installed backwards, an assembly problem I once experienced when Robar returned a newly NP3 plated BCG for my 6.5 Grendel with the bolt installed 180 degrees backwards so the extractor was in the 9:00 position rather than 3:00.

A friend had the same thing happen once, and it caused a jam (as the ejector tried to send the round out the solid side of the receiver) but did not result in a round staying in the chamber.

This sounds like a gas port issue. Try everything mentioned above.

How could it be the buffer or spring if the round is staying chambered?

Good luck.  The downside to assembling your own guns is that you are the tech support for your  work.  
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/03/2014 at 10:26
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I concur. Sounds like a gas issue of some sort.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/03/2014 at 10:35
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Had a similar problem with a customer build. Had a universal gas block with oversized port new everything but wouldn't cycle. After checkin and recheckin four times I discovered that when I pushed a drill bit shank first in the barrel port it didn't show in the bore. I had missed that the other four times. You could put the bit in drill point first and it would drop into the bore. But, if you dropped it shank first it would not go. A single burr was enough to obstruct gas. I cleared the burr and the thing cycled flawlessly. From now on that is one of the first things I check.

Also make sure that the gas tube is within the correct perimeters.

Good Luck!!




Edited by Sgt. D - July/03/2014 at 10:40
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/03/2014 at 10:36
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Also, remove the bolt and make sure the 3 gas rings are installed on the bolt piston. They could have been accidentally omitted.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/03/2014 at 13:15
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Originally posted by RifleDude RifleDude wrote:

Also, remove the bolt and make sure the 3 gas rings are installed on the bolt piston. They could have been accidentally omitted.


Or the three slots could be lined up letting the gas go by.

It could just be the rifle length gas system as well.  With a 18" barrel, they do not build up as much pressure.  I had an 18" WOA barrel with rifle length and I had to be picky with ammo for it to function right. 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/03/2014 at 23:55
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I had a burr in the gas port of the barrel on a new one once once removed its flawless.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/04/2014 at 06:41
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I had this problem with an 18" barrel and rifle length gas. The dwell time is too short once the gas gets to the port. After a great deal of research I found that .104" to .108" is a good size gas port for this setup. I drilled .106 and the problem went away. If you worry about going that big on the gas port, start opening it up a bit at a time until it functions (and continues to functions dirty).
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/04/2014 at 09:24
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Originally posted by mil169 mil169 wrote:

I thought I may have over oiled it. 


That's virtually impossible. You should see how wet I run my bolt on my AR. I dip the entire bolt in an oil bath and slap it in the carrier. More problems occur on an AR from NOT ENOUGH lube, then with too much...IMHO.   
Bubble Bath   
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/06/2014 at 11:50
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Originally posted by cheaptrick cheaptrick wrote:

Originally posted by mil169 mil169 wrote:

I thought I may have over oiled it. 



That's virtually impossible. You should see how wet I run my bolt on my AR. I dip the entire bolt in an oil bath and slap it in the carrier. More problems occur on an AR from NOT ENOUGH lube, then with too much...IMHO.   
Bubble Bath<span style="line-height: 1.4;">   </span>

Unless you live in a sand pit like I do. Mine stays pretty dry so it doesn't hold on to a lot of grit...
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/06/2014 at 11:57
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Probably so, Bill. Have you tried any dry lubes? 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/06/2014 at 15:16
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I have not. Kinda hard to get past CLP I used in the Corps. But I haven't done much research on any other lubes.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/06/2014 at 21:33
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Try some frog lube Bill. No need for clp after that. Its especially good in the dusty areas where dirt and grit are big problems
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/06/2014 at 21:54
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Finally got back to the problem upper tonight. The gas block set screw was perfectly lined up with the dimple and the gas tube was clear. Then I checked the gas port in the barrel. The port measured .104 using gauge pins, however, as Sgt. D suggested might be the case, the pin would not drop through the port and into the barrel. So after about 10 seconds wit the approriate drill, I removed the burr and the pin fit nicely all the way into the barrel. With that being said and the port being as big as it is, I would hope that now the gun will cycle as it should. I'll find out tomorrow.
 
As a side note. It seems the consenus is that rifle length systems can be finicky. Are mid length systems more forgiving as far as getting them to cycle reliably with a variety of ammo?
 
Thanks for all the suggestions.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/06/2014 at 22:54
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With 18" and 16" the mid length is better. 14.5 and less carbine. If you have a 20"+ the rifle seems fine as it has more time to push gas down the gas tube before it leaves the barrel. But that being said i had a 20" AR and it also had issues with some ammo. Personally i dont see the point in an AR with a barrel longer than 16" for most purposes. If it is for long range target shooting then i get it. But i shoot my 16" precision AR to 500 often and it works great. I built two 16" and one 18" with woa barrels several years back. The only thing the 18" did better was weighing more. :)

I have had 4 WOA barrels. All 4 of them had huge burs at the gas port. Kindof aggravating they dont even look down the barrels to check those things. My money goes else where now. There are other barrels just as good with out that issue. Sad to hear a Rainier barrel is like that.  I have two of them and did not have that issue.


Edited by supertool73 - July/07/2014 at 09:19
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/08/2014 at 08:02
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I got it to the range last night and it was not immediatly succsessful. It fired one round and then nothing, it did this with both Winchester and Federal 55 gr FMJ's and with Magpul and GI mags.
 
I put the upper on my lower, (same components and the one I just built), and it fired flawlessly for the rest of the mag. I put my upper on the problem lower, and it ran the first two shots fine, seemed to hiccup and was slow to close the bolt or something, but then fired fine and continued to function for the rest of the rounds.
 
I have no idea of what would be in a lower that would keep a rifle from cycling besides the buffer and spring. I thought those were dummy proof, but maybe not.
 
I put the new rifle back together and it shot fine for 75 rounds or so. I did have one light primer strike, but when reloaded it fired. I checked the hammer spring and it appears to be installed correctly.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/08/2014 at 14:41
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Check the inside of the problem buffer tube, make sure that it is smooth.  If you can, compare the buffer and spring from the "good" lower to the "problem" lower.  I would check length and weight, just to rule out issues.  You could also have some excess dragging on the hammer due to an out of spec lower or trigger components.  To check this, with the rifle assembles, pull the charging handle and pay attention to the amount of force used to cock the hammer, let the charging handle return and repeat.  There should be some resistance as the carrier drags on the hammer, but not much.  Try the above procedure again with the trigger pulled, this time there should be even less resistance as the disconnector will keep the hammer pulled further back.  If the resistance is equal to the first test you may have issues with the bolt carrier rubbing on the hammer and creating to much resistance.  Also check your hammer for excess wear. 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/08/2014 at 17:15
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Check your springs in hammer and trigger. Make sure the are installed correctly. I've seen them in the wrong and would act the same as your describing.
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