Hi, I just got in a 5.56 upper and am having issues with BCGs freezing right as it begins to go into battery. This happens with two different BCGs I have while one seems to work fine. Are PSA uppers normally picky with BCGs? One BCG I just purchased today because I was having this issue and is a Bushmaster mil spec M16 BCG. I took a look at all three BCGs and there are no glaring differences in dimensions and all seem to be in spec, just 2 out of 3 of them freeze right as the locking lugs meet the chamber and will not go into battery.
- are you riding the bolt home with the charging handle or letting it fly?
- are you using lube
- if neither of the above are issues then have you checked the headspace?
New bcg + new barrel = gtg
New bcg + old barrel = gtg
Old bcg with old barrel can be problamatic
Old bcg with new barrel also can be problematic
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I don’t have a set of no go gauges but the 1 BCG which has zero issues will close on a round in the PSA upper. The 2 BCGs which freeze in the PSA upper will not go into battery without force to even allow me to attach the upper and lower together. Yes, I have lubed them. BCG A it will work, BCG B it will freeze, BCG C is the brand new one and it freezes also.
I initially thought there might be an issue with BCG B so I disassembled it thinking maybe there was something I missed with the gas rings or cam pin because the bolt is a bit stiff moving inside the carrier. I found nothing that looked incorrect upon inspection. My best guess is perhaps there is some issue with the gas tube and gas keys on BCG B and BCG C. But both BCG B and BCG C work in non PSA upper.
Tolerance stacking is a thing. What brand bcgs are they? Also, can you post pictures as that might help.
I will try and get some pictures but I don’t know if they will help. Basically the BCG stops right as the bolt face begins to interact with the barrel extension. I’m unsure of the brand of BCG A, which works in both guns, and BCG B. BCG C is a Bushmaster milspec M16 BCG.
I figured since I found no issue with BCG B or BCG C themselves that the issue might be tolerance stacking. The PSA upper I ordered was one of the CHF barreled uppers and I found discussion on another forum about issues with reloaded cases in PSA CHF uppers due to tighter chambers.
My primary reason for the post was to see if anyone else had an issue with their PSA uppers being picky with BCGs? If tolerance stacking and pickiness is the issue then it is what it is and I will just have to find BCGs that don’t have an issue.
You can also try just the bolt (take it out of the full bcg) and see if you can hand fit it into the extension. If it goes in easily, then the issue is the carrier. If it doesnt, try the bolt less carrier in the upper. That may help you narrow down if it is the bolt or carrier.
Thanks I will give that a try.
Well I checked, bolt is not an issue, it appears to be the gas tube. When it begins to meet the gas key on the carrier it stops the carrier from moving froward. So perhaps the gas tube is out of spec and seated too far into the receiver. It doesn’t look out of spec to my eye.
There seems to be a minor variation in the geometry of the tube on the gas key that is almost imperceptible. The bcg on the left is A which works, on the right is C which is the Bushmaster.
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Do you have a fsb gas block or a lo profile under the rail one? If its a lo pro, take the rail off and visually check alignment as well as the tightness of the screws. Occasionally they can come loose and the gas block can shift.
Edit: that gas tube looks like the end is flared way more than it should be. That may have been caused by forcing the bcg home.
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i agree on the gas tube, i can post a comparison pic if you need one
might be an illusion, but looks like it sticks too far into the receiver
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If it is a lo pro gas block, it should not be snug up against the barrel shoulder. It should be just forward of it enough for your fingernail to fit. The gas tube isnt the wrong length (as no bcg would work) but im wondering if it is snug up against the shoulder, pushing it back just far enough to be a problem.
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The flare is an illusion of the light. It hasn’t been flare out. I will take the handguard off and see if that is the issue. It is indeed a low pro gas block.
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When I remove the nadguard this is what I’m looking at.
Gas block seems fine, no play or cant in it.
pic is of the barrel nut, look at the end of the gas tube itself you will see the gas block he is referring to
Yeah i meant to upload pic of gas block as well. It is not flush with the shoulder. Still a no go. On the bcg.
right on, does look correct
just so we’re clear…the BCG doesnt go into battery when you rack it, or just pushing it in by hand?
I can’t even get the bolt in to mate the upper and lower to try and let it go forward.
The best I can figure is that the gas tube and the gas keys on the two BCGs are just on the opposite ends of spec and dont want to play.
ohhh i see now