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Help me find the problem

Discussion in 'Black Rifle Forum' started by mmd, Mar 3, 2012.

  1. mmd

    mmd

    77
    0
    Mar 27, 2011
    My 2 friends have built the exakt same ar15 but one of the rifles dont work correctly.

    When we went to the range he loaded the magazine and put it in the ar15 and pulled the charging handle and fired the first shoot and then he tryed to fire the second round but the rifles just clicks. The hammer is cocked back and falls when i he pulls the trigger but its no new case in the chamber, im not even sure if it trows the old case out.

    Here is what we have tryed;
    Changed the gasblock/gastube, BCG, magazine and i think they have changed the lower to.

    I dont understand whats cusing this, i belived it was a gas issue but now i dont think that anymore. The only gas problem it can be is the gas port but would the hammer cock back without any gas?

    If the fired case is stuck it should be the extractor or can it be anything else? I think it trows the old case out but im not sure.

    If you have any idea how to solve this please tell me, even if you are not sure but think something can solve it.
    I would appreciate it
     
  2. WoodenPlank

    WoodenPlank Who?

    7,958
    3
    May 15, 2010
    NW Florida
    If there's no empty case stuck in the chamber or bolt raceway, then it's being ejected.

    I've seen the same problem before when a rifle-length recoil spring ended up in an AR with a carbine buffer tube and carbine buffer. What weight buffer do you have in each rifle? Take the buffers and buffer springs out, and count the number of coils. A rifle-length spring has 44 coils, and a carbine spring has 39. It's 34/34 in an .308, I believe.
     

    Last edited: Mar 3, 2012

  3. DJ Niner

    DJ Niner Moderator

    15,036
    805
    Feb 13, 2001
    North-Central USA
    Check the bolt carrier for loose gas key screws, and the bolt for broken/missing gas rings; either of these could allow loss of enough gas to cause the problem you are seeing.

    Swap the bolt carrier group from another gun that functions properly, into the one that's having problems. If it runs fine with a replacement bolt carrier group, then the problem lies with the original bolt/carrier/parts.
     
  4. WoodenPlank

    WoodenPlank Who?

    7,958
    3
    May 15, 2010
    NW Florida
    These, as well.
     
  5. mmd

    mmd

    77
    0
    Mar 27, 2011
    What is bolt raceway?

    We have tryed to change the BCG and it still have the problem.

    Its a carbine buffer tube and spring and carbine buffer.
    Can it be that the buffer tube is screwd in to much?

    What cant it be if its not the BCG?
     
  6. WoodenPlank

    WoodenPlank Who?

    7,958
    3
    May 15, 2010
    NW Florida
    Did you count the coils on the spring to be sure?

    If you swapped a known good BCG, and the problem continues, then it's probably a gas issue. Either the gas port is partially blocked, isn't drilled the right size, or something's wrong with the gas tube. It COULD be bad/weak ammo, too. If the known good rifle runs the same ammo without problem, though, then it's not ammo.

    Edit: Bolt raceway is basically the upper receiver and buffer extension - the areas the bolt moves through during cycling. if you're not finding empty brass in the gun, then it's definitely ejecting it.
     
    Last edited: Mar 4, 2012
  7. Gunnut 45/454

    Gunnut 45/454

    12,129
    9
    Jun 20, 2002
    My question is what ammo? Try full powder XM193 or IMI193 and see if the problem exists. You didn't mention changing the Mag. That should have been the first thing done. Not picking up the next round is call short stroking! Usually caused by underpowered ammo, bad mag, or wrong spring /buffer combo.
     
  8. WoodenPlank

    WoodenPlank Who?

    7,958
    3
    May 15, 2010
    NW Florida
    I've (personally) never seen or heard of it being caused by a magazine issue...
     
  9. BBJones

    BBJones

    1,173
    0
    Mar 2, 2010
    Since you have swapped uppers and problem persisted with the one lower I would bet on buffer, buffer spring, or buffer tube being the culprit.
     
  10. WayaX

    WayaX Lifetime Member

    2,551
    24
    Feb 27, 2007
    You say "built" so I assume these are home brews. Do you know what parts they put into the lower (especially concerned buffer, action spring, and receiver extension)?

    Of course, you say they changed lowers...

    If the rifles are "identical", and one is working and the other isn't, then they aren't identical.

    Who made the barrel, and what gas length?

    Make sure they haven't fallen into this trap:

    http://www.m4carbine.net/showthread.php?t=62635

    It sounds really stupid, but it comes up more often than one might think.

    You say you changed the gas block, so I'll assume you probably are using a screw on gas-block. Are you positive you're aligning it correctly?

    All the other suggestions here are good too.
     
  11. WayaX

    WayaX Lifetime Member

    2,551
    24
    Feb 27, 2007
    It can be caused by an over-gassed rifle with a very weak (or malfunctioning) magazine spring. This isn't very common, but it is possible.

    Of course, I read the OP changed magazines. It is worth asking what ammo the OP was using.
     
  12. mmd

    mmd

    77
    0
    Mar 27, 2011
    I dont think the rifles eject the fired case.
    I have tryed a BCM BCG and FN.
    I have drilled the gasport a little bigger maby 0.01" bigger.
    Its a screw on gasblock.
    Its carbine gastube and a carbine lenght barrel. One problem is that barrel dont have a dimpel under the gasport so its hard to know that you are 100% aligned but im pretty sure that when changed the gasblock it was alinged.
    Its a carbine buffer/spring/tube.

    I will try to meet him tomorrow and take alot of photos.
    Can it be something wrong with the upper reciver? The charging handle have scratches on one side. I will try a new magazine next time but it cycles when he pulls the charging handle. This is sick, i have never herd of this.
    Im thinking that he maby should re-assembly everything
     
  13. WoodenPlank

    WoodenPlank Who?

    7,958
    3
    May 15, 2010
    NW Florida
    You haven't mentioned what kind of ammo is being used.

    Attempting to ream out the gas port is ALWAYS an absolute last resort - screwing it up can be catastrophic for the rifle.

    Is the gas-block a set-screw type (ie: screws press against the barrel, block is a single piece) or a clamp-on (ie: block is in two distinct pieces - upper and lower - and screws hold them together)?

    If you are even the least bit unsure of the gas port and gas block alignment, take it (or ship it) to a gunsmith that specializes in ARs and have it checked out.

    The scratches on the CH can be caused by repeated one-handed manipulation of the charging handle (ie: using your left palm to yank the CH to the rear), especially when using a standard handle with an extended latch.
     
  14. country85

    country85

    249
    0
    Jan 14, 2012
    Greentown, IN
    I ran into this problem at the range today, I just got a 20 inch heavy barrel upper and haven't got a rifle stock/tube yet so I was shooting it with my carbine buffer and tube. I'm hoping putting an A2 rifle stock assembly(with A2 buffer and tube of course) will solve the problem. Hey until then I've got one cool looking straight pull bolt action rifle lol. Also might want to check your gas rings on your bolt to make sure the gaps aren't lined up. It's a good idea to have the gaps about 60 degrees away from each other(make sure that none of the gaps are lining up)
     
  15. WoodenPlank

    WoodenPlank Who?

    7,958
    3
    May 15, 2010
    NW Florida
    A 20" upper will run fine on a carbine stock system, assuming you're using actual carbine parts. If you put a rifle spring in that carbine tube, you'll end up with a straight-pull bolt action real quick.
     
  16. faawrenchbndr

    faawrenchbndr DirtyThirty fan CLM

    36,074
    441
    Nov 24, 2005
    Troy
    OP

    Load one round into a mag and test fire,.......does the bolt lock to the rear?

    Also,........with a Carbine, drilling the gasport is a VERY bad idea.
    They are over gassed as it is from the factory!
     
    Last edited: Mar 6, 2012
  17. WoodenPlank

    WoodenPlank Who?

    7,958
    3
    May 15, 2010
    NW Florida
    ...and if it does, is the bolt catch grabbing the bolt carrier itself, or the bolt face? It should be catching the bolt face, NOT the carrier body.
     
  18. mmd

    mmd

    77
    0
    Mar 27, 2011
    he use barnul ammo. Russian cheap ammo but it works in my ar15 and everybody else.
    I try to load one round.
    Whats wrong if it locks on the carrier and not the face??
    This is really irritaing
     
  19. WoodenPlank

    WoodenPlank Who?

    7,958
    3
    May 15, 2010
    NW Florida
    Cheap Russian ammo won't run in every AR. Short stroking can be a sign of weak, crappy ammo - exactly what it's being fed.

    If the bolt catch is snagging the carrier itself when shooting, then your bolt is not coming back all the way. This would also be why you're getting ejected empties, but no round loaded in the chamber.

    Since you said you'd already checked the buffer and action spring, it's most likely the simple fact that that particular upper does not like the cheap, underpowered ammo. Try running some Federal XM193 through it and see what happens.
     
  20. Gunnut 45/454

    Gunnut 45/454

    12,129
    9
    Jun 20, 2002
    WoodenPlank
    Bingo we have a winner! Get some good ammo-XM193, IMI193, AE223 etc try again and see if the problem still exists! I'll put money on it that it disappears! Cheap Russian ammo- problems!