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Posted: 2/27/2012 11:35:47 AM EDT
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I'm fighting an issue I've been having with my ar build. Please throw out any possible suggestions or ideas that might have any possibility of solving my issue. I've tried everything I know.
Heres the rifle specs: Upper assembly is composed of : RRA flat top upper RRA bcg Daniel defense 12" lite rail Noveske SPR 18.5" 5.56 barrel vortex flash hider The lower is a completely stock RRA Lower with Single stage and collapsible stock. The rifle will shoot up to 3-5 rounds before failing to load another shell then have to manually charge it. I know its short stroking by finishing off a mag and the bcg doesn't lock open. I'm 90% sure (just to cover my @ss) the gas block is seated properly and aligned. I've tried different brands of 55 gr ammo and 69 gr ammo ( mostly black hills and Remington) and switched between standard mags and pmags with no avail. I'm stumped. Thanks for any suggestions. |
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What buffer are you running. Standard or heavy buffers?
Make sure also it is rare that it happens but make sure your gas tube in the upper is not bent, make sure the bolt if lubed up very well, and also check that the bolt moves (tight) but moved in the carrier. |
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I'm not sure what buffer I'm running. It's the buffer that RRA puts in the lower at the factory, I haven't touched the lower in anyway. Any recommendations on a different buffer to try?
As far as lube, I just have a light coat of oil on it. Any suggestions here? The gas tube in the upper doesn't appear to be bent ( I dont have the rifle with me at the moment but did check that the other day), the bolt does move tightly in the carrier. Thanks again for the advise, I can't wait to get this shooting 100% |
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Also check to make sure your gas key on your BCG is properly installed... I'm assuming you don't have a Noveske switchblock right? I think the gas key should be okay, I bought a complete BCG from RRA and haven't touched that either. I'm not using the switchblock, just their low profile gas block. |
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@ dylang32
I will lube it up next time I go shooting and pick up some 5.56 ammo, thats good to know about the hotter loads. I've been shooting mostly black hills 69 gr re-manufactured. Obviously I'm not getting enough pressure since when the BCG locks open the bolt catch catches it in between the carrier and bolt instead of properly catching it at the front of the bolt. Thanks for the tip |
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Is the gas block positioned correctly 100%? to the best of my knowledge the gas block is on perfect, I took my time on that step to get it as close as possible. I reset the gas block once already thinking that was the issue and it was previously lined up perfectly by the carbon build up on the barrel where the gas block hole overlapped the hole through the barrel. At this time I feel pretty confident I can eliminate that factor from my problem. |
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It is likely the gas block not lining up with the gas port in the barrel (which is often from the barrel not being drilled perfectly perpendicular in relation to the barrel extension). If you remove the gas block, you will see burn marks on the barrel in the shape of the hole in the gas block (which is typically much bigger in diameter). If it was properly lined up, then you may need to open your gas port up. ETA: you posted your answer to this before this posted.
Check the tube and gas key to see if there is an obstruction somewhere in your gas system. Another thing you might check is if the magazines are properly seated in your magwell (i.e. they are high enough to consistently have the bolt catch the next round and the BHO end of the follower). Lastly, you might check to see how tight your gas rings are. If they are extremely tight (requiring 20+ pounds to press down your bolt into your BCG on a table, you might take them off and compress them slightly and put them back on. |
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It is likely the gas block not lining up with the gas port in the barrel (which is often from the barrel not being drilled perfectly perpendicular in relation to the barrel extension). If you remove the gas block, you will see burn marks on the barrel in the shape of the hole in the gas block (which is typically much bigger in diameter). If it was properly lined up, then you may need to open your gas port up. ETA: you posted your answer to this before this posted. Check the tube and gas key to see if there is an obstruction somewhere in your gas system. Another thing you might check is if the magazines are properly seated in your magwell (i.e. they are high enough to consistently have the bolt catch the next round and the BHO end of the follower). Lastly, you might check to see how tight your gas rings are. If they are extremely tight (requiring 20+ pounds to press down your bolt into your BCG on a table, you might take them off and compress them slightly and put them back on. The gas rings are just tight enough to support the BCG weight if I were to stand it up on the table (the bolt would stay fully extended and not slide into the BCG) I think the mags aren't causing it, I have tried two different lowers on this upper that shoot flawlessly on other uppers with the same mags. Is there any rule of thumb on what kind of buffer you should use for a carbine, mid-length, rifle gas system ? Or in my case the intermediate gas system? Or does it even matter? |
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I would bet that you have a standard buffer (CAR) as RRA original equipment. That's the lightest carbine-type buffer.
Your symptoms would implicate gas block misalignment (you say that's OK) or under-powered ammo. I highly doubt that the Noveske gas port is under sized. For the next check I would run some full power ammo like Lake City XM193 or M855. (running Remington and the reloads, it's a good bet that this will fix it) If that fails to properly lock back on an empty, known-good mag I would revisit the entire gas system. |
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It may be worth mentioning that the barrel comes with a pinned gasblock which I have taken off and can confirm it straddles the gas hole perfectly.
Im glad you guys mentioned some hotter loads to run through it, I wouldn't have known of any to try. It sounds like that may be my ticket (hopefully it is). Then it makes sense why the gun will work correctly and sometimes short stroke the other times. I've spent quite a bit of time with my other bolt rifles behind a chrony with factory ammo and the velocities are wildly inconsistent when compared to hand loads. Thanks to all for the input, I can't wait to give it a go. Unfortuantely it will be a while until I can make it back out to the range. 
Please send any more suggestions you guys think of this way, I'm game to try anything as I'm itching to get this gun working correctly. |
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Being you have tried other working lowers, I'm thinking your buffer/lower group isn't an issue. You can verify that by trying your lower on a working upper though. Sounds like possibly a gas problem. Either gasblock alignment, port size, underpowered ammo. I would think both brands of ammo you are using are sufficient for proper operation though.
Is it possible something is mechanically dragging, slowing down carrier velocity? Does everything in your upper move freely? You might try another BCG in your upper. Maybe something out of spec, dragging on hammer. All just speculation of course. Good luck. |
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I would think both brands of ammo you are using are sufficient for proper operation though. Actually no. Both of those ammos would go immediately into the suspect file. Factory first run XM193 or M855 would be the test ammo that we need for this rifle. I have several BCM carbines and middies. BCM is known for minimum port size and both those kinds of ammo function fine in my rifle. Not saying this isn't aggravating the problem, just saying it "should" work with it. It ain't Tula... |
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If you have another functioning lower, try that on the upper and then you will know it isn't magazine related or anything to do with a bad bolt catch or mis-aligned buffer system. EDIT: doubleajaybrock beat me to it.
Have you hand cycled a mag or two? If it does it while hand cycling, then it definitely isn't the gas system. It sucks to do, but if you take out the little roll pin holding in the gas tube in, you can check to make sure the tube and the block aren't obstructed with any chunks of metal or carbon. The only other thing that I can think of is that maybe there is too much of a gap between the BCG key and the tube (maybe it is a midlength with a carbine tube?). |
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I have eliminated the lower by firing with known working mags on one working upper and it worked great. Then moved back to the problematic upper and back to short stroking. I also switched lowers as mentioned. The problem definitely lies within the upper assembly. I have checked the tube and it is clear of any debris.
That is a huge PITA  Taking the Lite rail off takes forever with a hand wrench since you can only get an eighth of a rotation in before you have to reset your wrench.
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Being you have tried other working lowers, I'm thinking your buffer/lower group isn't an issue. You can verify that by trying your lower on a working upper though. Sounds like possibly a gas problem. Either gasblock alignment, port size, underpowered ammo. I would think both brands of ammo you are using are sufficient for proper operation though. Is it possible something is mechanically dragging, slowing down carrier velocity? Does everything in your upper move freely? You might try another BCG in your upper. Maybe something out of spec, dragging on hammer. All just speculation of course. Good luck. This is what I was thinking. |
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Being you have tried other working lowers, I'm thinking your buffer/lower group isn't an issue. You can verify that by trying your lower on a working upper though. Sounds like possibly a gas problem. Either gasblock alignment, port size, underpowered ammo. I would think both brands of ammo you are using are sufficient for proper operation though. Is it possible something is mechanically dragging, slowing down carrier velocity? Does everything in your upper move freely? You might try another BCG in your upper. Maybe something out of spec, dragging on hammer. All just speculation of course. Good luck. This is what I was thinking. I'll give that a try as well. I THINK, I'm not sure if I remember correctly, that I fired the BCG in another functioning AR and it worked flawlessly. This was all tested in a mid length which would yield higher pressure than my 'troubled' intermediate upper |
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When the rifle fails is the chamber empty or is there a fired case in the chamber? If the second case, stick an o-ring under the extractor and try again for testing. As in put an O-ring inbetween the bolt and the back of a shell case and fire?? 
Sorry I think I may have misunderstood you. Wouldn't that yield melted O ring blown into my BCG? When it fails, it doesn't come back far enough to load another shell so it is empty. |
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When the rifle fails is the chamber empty or is there a fired case in the chamber? If the second case, stick an o-ring under the extractor and try again for testing. As in put an O-ring inbetween the bolt and the back of a shell case and fire??
Sorry I think I may have misunderstood you. Wouldn't that yield melted O ring blown into my BCG? When it fails, it doesn't come back far enough to load another shell so it is empty. Most rifles with a good extractor, spring and insert don't need the O-ring fix. You didn't say anything about about extraction issues so I wouldn't worry about it. I think I have a pic to show it for reference.... Extractor O-Ring Top = extractor, spring and less desirable blue insert Bottom = extractor, spring, preferred black insert and O-ring installed Use the black insert and a good spring and chances are you won't need the O-ring. |
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@ Direct-Drive Thank you for the clarification. The gun is extracting and ejecting fine so I think I'm okay in that aspect. It's a 2 step process. The extractor is the "hook" on the side of bolt that grabs the case rim. (in my pic) The ejector is the little spring-loaded "post" in the bolt face that kicks the spent case out of the receiver as the extractor draws the case back. Mr. Stoner designed a fine weapon. |
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@ Direct-Drive Thank you for the clarification. The gun is extracting and ejecting fine so I think I'm okay in that aspect. It's a 2 step process. The extractor is the "hook" on the side of bolt that grabs the case rim. (in my pic) The ejector is the little spring-loaded "post" in the bolt face that kicks the spent case out of the receiver as the extractor draws the case back. Mr. Stoner designed a fine weapon. Thank you for the clarification, its rather similar to a Remington 700 action which I'm fairly familiar with. I like the ar15 but I got my eye on an ACR.  Always always something new to spend your money on. 
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