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AR15 Failure to Extract

Discussion in 'Maintenance & Gunsmithing' started by PBinWA, Apr 4, 2010.

  1. PBinWA

    PBinWA Clark County Well-Known Member

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    I'm building my first AR-15 and am having a Failure to Extract issue.

    I found this thread on thehighroad.org with this description which seems to be an accurate description of what is happening:

    http://www.thehighroad.org/showthread.php?t=407909


    It's a 14.5 Barrel (with pinned+welded flash hider) brand new BCG etc. Everything appears to be tight and it ejects when manually cycled.

    I'm thinking it's the Buffer. I'm just using whatever came with the CAA CBST stock - but can't tell what weight of buffer it is. I don't think I have a scale that can weigh it accurately.

    Any other suggestions? Should I go with the H2 Buffer and see where that gets me? Should I go straight to the H3 Buffer?

    Any advice appreciated.

    PB

    What do you more experienced builders recommend? The H2 or the H3 Buffer.
     
  2. Riot

    Riot Benton County, Washington Well-Known Member

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    Gas tube rings...check those first. Then run a pipe cleaner down the gas tube...if you can manually cycle it, then it sounds like the gas isn't pushing the bolt hard enough back.

    You may be right on about the buffer as well...did you replace the stock? Replacing the stock from the fixed stock to a 6/8 possition stock requires the buffer to be replaced as well to the carbine buffer.
     
  3. dave

    dave Independence Member

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    Yeah that ^^^^^^. The tube might just need to be clocked so the gas is going through the block to the tube also. If the gas tube is not lined up with the hole in the gas block, no gas pressure will blow back to the bolt.

    I explain things about as well as Charlie Browns teacher. Type in Gas block in Youtube and get a much clearer example.
     
    Last edited: Apr 4, 2010
  4. PBinWA

    PBinWA Clark County Well-Known Member

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    Nothing has been replaced. It's a new stock. It's my first AR build so nothing is too high end - I knew I might have to redo something.

    It's the Command Arms stock and came with a tube, spring, and buffer. It doesn't tell me what type of buffer though:

    http://www.commandarms.com/product.asp?pID=278&cID=57

    The gas tube is new and I'm pretty sure everything is all lined up. I flushed the tube with gun scrubber once I pinned it to the block to make sure it was clean before attaching it to the barrel.

    What's the procedure for verifying that the gas block is lined up properly with the hole in the barrel?
     
  5. bnr32gtr

    bnr32gtr Vancouver, WA Member

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    What BCG do you have? Before tearing everything apart and blaming the gas tube(I've NEVER seen a clogged on) and the buffer(not a common cause in short stroking).

    Pics and a FULL description of the build including manufacturers of the parts would help us help you.
     
  6. Riot

    Riot Benton County, Washington Well-Known Member

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    Again, gas rings first...and I've seen the buffer the cause when you use a full stock buffer vs a carbine buffer.

    Full Sized Stock Buffer (for fixed stocks)

    Carbine Buffer (for 6/8 possition stocks)


    If the gas rings line up to make on straight hole from top to bottom, then that will do it. They should be staggered to form three different holes. If they seam too loose, then just give them a little tighten with a leatherman...or just replace them (since this part is probably the cheapest to replace). This is the number one cause of FTEs I've seen in ARs, M-4s and M-16s.

    gasrings.jpg
     
  7. PBinWA

    PBinWA Clark County Well-Known Member

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    I kind of collected parts when they were on sale so as I stated before it's a learning experience and I didn't want to buy high-end stuff for something that I will be learning on.

    SI Defense Forged Upper, 14.5 Barrel, and BCG.
    Spike Tactical Lower.
    Timberwolf Tactical Stainless LPK
    Hogue grip and forearm and gas tube.
    Basic Gas Block (http://shop.si-defense.com/Modular_Gas_Block_Stripped_Black_750_Diameter_p/si-mod-gb-750.htm)

    I think that's everything.
     
  8. PBinWA

    PBinWA Clark County Well-Known Member

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    Thanks Riot - it's definitely a carbine buffer.

    I'll have to take the BCG apart. It came assembled since I was hoping they would be better at that part than me but I can certainly give it a try. Since I had the SI Defense upper I went with their barrel and BCG. I was kind of hoping that would make things easier. :eek:
     
  9. PBinWA

    PBinWA Clark County Well-Known Member

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    I took the BCG apart based on this video (http://www.youtube.com/watch?v=t0J_zvWEnzw) and everything looks pretty close to the video and there was no straight hole through the rings.

    AFAIK - it looks right. (not that I know for sure).
     
  10. wichaka

    wichaka Wa State Well-Known Member

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    Contrary to popular belief, lined up gas rings won't cause anything but anxiety from people on the internet.
     
  11. bnr32gtr

    bnr32gtr Vancouver, WA Member

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    Thank you! The rings seal on the bolt carrier and while important, don't usually cause a failure to eject.

    To the OP, what did you use to keep the screws in the gas block? Loctite, Rocset, Vibratite?

    If the barrel's gas hole is not big enough, you will get short stroking. If the gas block is not lined up directly over the gas port on the barrel, you will get short stroking.

    I also looked on the SI Defense site and it did not say what parts are used in the extractor assembly. Red insert, black insert, D-Fender?
     
  12. PBinWA

    PBinWA Clark County Well-Known Member

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    I used loctite on the screws. I took it off last night and could see a ring from the gas around the hole that looked like it was pretty close to centered.

    The one thing I noticed is that the gas block is not very snug on the barrel. How snug should they be before you tighten them? Should they spin freely?

    I'm going to say "black insert" on the extractor assembly - I didn't see anything red in there and I didn't see this in there

    The extractor appeared to be just a spring no gasket. I'll try to snap a picture later this morning.
     
  13. usfatboy01

    usfatboy01 Hillsboro, Oregon Member

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    Not reading the thread, but what caliber is it chambered for. It will and can make a difference. .223 vs 5.56. 5.56 will handle both, .223 will only handle .223. 5.56 is a little higher pressure. Just a ?.
     
  14. goneshooting

    goneshooting Oregon City Member

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    i did not read all replies so not sure if its been resolve but your gas block may not be aligned with the gas port correctly if its off a little bit you wont get enough gas

    if the bolt is going back and leaving the brass in the chamber then it could be you want to polish the chamber
     
  15. PBinWA

    PBinWA Clark County Well-Known Member

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    1/8 twist chambered in .223 Wylde - I was shooting some Remington .223 in 55 grain.
     
  16. PBinWA

    PBinWA Clark County Well-Known Member

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    I'm thinking it's the loose fitting gas block. I think once it is tightened on the barrel by the bottom screws there has to be enough space for gas to escape.

    Any tips on polishing the chamber?
     
  17. PBinWA

    PBinWA Clark County Well-Known Member

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    Here's a close up of the extractor assembly. I didn't really clean it up too much. I just gave it a shot of Rem Oil and wanted to see if everything worked. I was planning on a more detailed cleaning once it was all functioning.
     
  18. PBinWA

    PBinWA Clark County Well-Known Member

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    Well, like most things in life I'll throw money at the problem and see if I can figure it out.

    I ordered a YHM Gas block, and upgraded extractor spring kit, and an H2 Buffer.

    I'll throw all these things in when they show up and see what happens.

    I like the idea of polishing the chamber a bit too. It's pretty snug so maybe a little polishing would help. If time permits I'll see what I can do.

    Thanks all.
     
  19. goneshooting

    goneshooting Oregon City Member

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    I would start with the gas block if that dont fix it i'll have a buddy of chime in he had to do it with a newly cut custom chamber that had extraction issues you will know this is a probable if the bolt is going back but leaving the case in the chamber after firing ,

    and a extractor insert or o ring wont fix the problem polishing should not be done unless necessary

    noticed you don't have the little blue or black insert in the extractor this is a which is a item that cost more to ship that it actully cost ($1) this will also cause it to leave the case in the chamber

    if there is room for gas to escape that IS your problem

    also make sure the gas port in the barrel is properly aligned with the gas port if the glass block if not if may not be getting enough gas this will cause short stroking meaning the extractor has hold of the shell but does not go back far enough to eject it
     
  20. bnr32gtr

    bnr32gtr Vancouver, WA Member

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    What GB did you order? I have one sitting here at the house we could try tomorrow, if you like. I need to go shooting anyhow. If you want it, it's yours. Just replace it with the one you ordered.

    I'll be at my shop after about 2pm in Portland if you want to come down and work on the gun, then test it tomorrow. I have snap caps to function test with before we hit the mountain. :thumbup:

    Mike 503.819.6166