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Some ar upper help.... Please

Discussion in 'Maintenance & Gunsmithing' started by mike1281, May 16, 2016.

  1. mike1281

    mike1281 Canby Member

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    Ok so I built my first upper. It 20inch, so rifle length gas tube and a low profile gas block. I made the mistake of buying a cheap Chinese low profile block and realized none of the gas holes seem too line up just right. So I chucked that and bought a steel one from cobra tac. Everything lined up as it should. So I took it out and It fires the first shot just fine. It eject the shell and won't load next round. Tried different mags, same problem. The lower I put it on and BCG I know are in good operating condition as I have had em for years and never had a problem. Stripped upper was bought from aero. Rifle gas tube is Brownells. Barrel is a spinta precision.

    I began to disassemble this morning to look for the problem and I see a leak at the gas block. I will post pics. Your thoughts on what I should do next would be much appreciated.

    image.jpeg image.jpeg
     
  2. mike1281

    mike1281 Canby Member

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    It's seems some things I have read online but I really don't know, is that this is normal and will seal itself off eventually.
     
  3. PDX1953

    PDX1953 Active Member

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    AR15.com is quite possibly the best source of information for AR's & AK's, among other things. I've learned WAY more on that site than I could by trolling a gaggle of other sites. Great, friendly advice to boot.

    Best of luck.
     
    erudne, PiratePast40 and mike1281 like this.
  4. Garg

    Garg east of portland metro Hold my beer..... watch this Bronze Supporter

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    What kind of bolt carrier. FA or semi?
     
  5. Reno911

    Reno911 Hillsboro Well-Known Member 2015 Volunteer 2016 Volunteer

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    That gas residue is not as much of a leak as it is normal wear on a new gun. Your tube and block will gunk up eventually sealing them together. If they were an exact fit you wouldn't have been able to slide them on or into each other.

    It does sound like you are short stroking though.

    I ask these questions every time to get a better picture.

    What ammo?

    Buffer weight?

    Size of the gas port on the barrel?

    I don't see any major issues so far so it is likely the gas port size not allowing enough gas to cycle the action.
     
    Garg likes this.
  6. mike1281

    mike1281 Canby Member

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    I really appreciate your guy's response! So its a FA BCG. Was using a few different kinds of ammo at the time 55g PMC and 55g AE then for the helluva it tried a couple 62g Tula. None performed any better than the other. Lower has a carbine buffer. (Buffer issue?) Not sure exactly on gas port hole right now. Would need to disassemble further and measure. What should that port hole be? Thanks again!
     
  7. Reno911

    Reno911 Hillsboro Well-Known Member 2015 Volunteer 2016 Volunteer

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    Just taking s guess at the port hole because of the barrel manufacturer. I've never heard of them, and in the past smaller companies with inexpensive barrels where known for head spacing issues and gas ports being too small and such.

    I used to have a list of proper sizes for ports per barrel length and gas length. I'll see if I can pull it up and get you what it should be.

    Either way. Your gun needs more gas. So if you check and recheck the alignment of everything, your using good ammo, and a light buffer. I'd point to the gas port.

    That is of coarse there is no obvious defects noticed. Like binding bolt carrier in the receiver type thing.
     
  8. rick benjamin

    rick benjamin USA, Or, Damascus Secure the drama Silver Supporter 2016 Volunteer

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    gas port sizes

    gas port size chart.jpg
     
  9. mike1281

    mike1281 Canby Member

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    Yeah I just took it all apart. measuring with calipers I am getting my port hole @ .07 in. My barrel diameter is .750. Distance from muzzle is 6.875. So looks like my port size is a problem
     
  10. rick benjamin

    rick benjamin USA, Or, Damascus Secure the drama Silver Supporter 2016 Volunteer

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    Does a 5/64" (.0781) drill bit enter the hole?
     
  11. mike1281

    mike1281 Canby Member

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    Yes. I don't trust my measuring of the hole now:rolleyes:.
     
  12. Reno911

    Reno911 Hillsboro Well-Known Member 2015 Volunteer 2016 Volunteer

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    If bump it to a 3/32" or a #42 bit and see how she does.
     
  13. mike1281

    mike1281 Canby Member

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    And that's the sizing missing from my bit set.... LOL I will pick one up and let u know
     
  14. mike1281

    mike1281 Canby Member

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    3/32.... It fits
     
  15. Medic!

    Medic! What just happened? Has eagle eyes. But cant remember what he saw. Bronze Supporter

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    If you load a single round into a magazine and shoot it.
    Dose the round eject and the bolt lock back on the empty mag?

    If so you have enough gas and need to look else ware.
     
    uscsoldier and B5Ben like this.
  16. mike1281

    mike1281 Canby Member

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    Yeah it never locked back on the last round. Even after taking it apart now. I can see with the carbon build up, that the block is aligned properly. Perhaps I should try a new gas tube?
     
  17. Medic!

    Medic! What just happened? Has eagle eyes. But cant remember what he saw. Bronze Supporter

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    I know you said the bolt carrier group is good.
    But is it leaking at the gas key[Bolts loose]? And sealing right at the rings? Is the gas tube protruding far enough into the gas key?
     
    Last edited: May 16, 2016
  18. Reno911

    Reno911 Hillsboro Well-Known Member 2015 Volunteer 2016 Volunteer

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    Well your port sounds like it is correct size.

    Your block could be bleeding off too much gas.

    Try lock tight between the barrel and the block and a little around the tube and block.

    Might help.

    If not.

    Double or triple check to make sure nothing is binding. Things like the cam pin. Or make sure your buffer didn't come apart in you recover extension. Make sure nothing else is in your receiver extension.

    If the gun still fails all those. I would still the port one size larger until it cycles. :cool:
     
    mike1281 likes this.
  19. mike1281

    mike1281 Canby Member

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    What would I look for in a leaking gas key? And how do I tell if the tube is inserted far enough into the key?
     
  20. mike1281

    mike1281 Canby Member

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    Blue or red?