Pennsylvania Firearm Owners Association
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  1. #31
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    Default Re: AR Failure to Feed - Please Read

    ianb1116

    1) An extra heavy spring will likely not solve your problem. If you're under gassed and not getting enough power moving forward, a heavier spring may only exacerbate this. If it only happens when dropping the bolt, an extra power spring may help. However, more than likely, just sitting in front of the tv manipulating the charging handle a million times will solve any issues by wearing the parts into each other (read: reduce friction).
    2) What do the feed ramps look like? Does the barrel extension have m4 ramps? Does the upper?
    3) How many cycles (approx.) has this new upper seen? Some bolts have extra thick coatings and truly need a break in period.
    4) Is the barrel freefloated? If so, what kind of gas block? Have you taken this off to check for obstructions to the gas port? What about port/block alignment? Again, this only applies if it FTF's during live fire.
    5) Have you inspected the bolt gas key staking? If the staking is poor and the key is loose, this could cause your problem.
    6) Does your failure look like this: http://www.ar15.com/forums/t_1_5/128...e_to_Feed.html
    7) How much lube/oil are you using? A new gun likes to be dripping until loosened up a bit.
    8) Have you tried dropping the bolt on 29 rounds? 28? 27? 3? 2? 1? Spring tension in the mag may be overcoming buffer spring expansion forces.

    In Order:

    1) Only happens on the first rounds when dropping the bolt on the first round. Live fire cycling isn't an issue.

    2) Has M4 feed ramps, factory from Palmetto State Armory (PSA).

    3) 1,000 plus cycles through this gun. Not new, but not old. Also shooting a nickel boron coated BCG from PSA.

    4) Barrel is floated - but I haven't tore it apart or checked the gas block....ever....bought the upper pre assembled from PSA direct.

    5) Have not checked bolt gas key staking. Need to look in my manual for that, to be honest, not even sure what that is (here is my ah-ha moment and why I am happy I posted this! Learning new $%# everyday!)

    6) Yes - that is EXACTLY what my FTF looks like on the initial bolt drop from a newly loaded mag. Every dang time.

    7) Generous amount oil during use and then reapplying a light coat after cleaning. I am not shooting it dripping wet though. Type of oil varies. Used some Weapon Shield and loved it.

    8) I've read about this and tried 29 rounds, etc - but still seeing and issue. Haven't tried less though - punted on the idea after the error occurred when I loaded 29.

  2. #32
    Join Date
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    Mohnton, Pennsylvania
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    Default Re: AR Failure to Feed - Please Read

    Quote Originally Posted by TetsuFury508 View Post
    No sling shotting or riding the bolt. When we shoot 3 Gun - they want your bolt back showing an open chamber. So you enter the stage, grab your empty gun, load the mag, and then I drop the bolt.

    @Rosco - I am not an expert, thats why I am on here asking.

    @Gunsnwater - Interesting, so the heavier spring would slow the BCG after I fire the first round. Is that what you mean? More resistance against the BCG coming back because of the heavier spring, which would slow it down. Right?
    Yes cyclic drops with heavier spring.

  3. #33
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    Default Re: AR Failure to Feed - Please Read

    Alright, so I am reading more....

    If the spring slows down cycle rate and doesn't provide enough effective energy as I am thinking it might - then adding more mass to the buffer assembly, should. Right?

    Standard carbine buffer weight is 3.0 oz factory. From what I've found I can go all the way up to 8 oz (I think thats overkill though). Colt offers three weights - 3.8/4.6/5.4oz

    More expensive of a fix (seeing weights range from $30 to $130) but if this fixes it then its worth it!

  4. #34
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    Jun 2010
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    Default Re: AR Failure to Feed - Please Read

    Figure out what buffer you have first. Most buffers are marked somehow, usually on the face of the buffer. No marking 3oz carbine buffer, "H" = H buffer, "H2" = H2 Buffer, "H3" = H3 buffer, etc.

  5. #35
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    Default Re: AR Failure to Feed - Please Read

    Will do, I have to drive up to Butler to get it this week. Will report back with my findings later this week/weekend

  6. #36
    Join Date
    Apr 2007
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    Pittsburgh, Pennsylvania
    (Allegheny County)
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    Default Re: AR Failure to Feed - Please Read

    It has to be a combination of the bolt carrier group spring tension and the mag's spring tension on the rounds. The BCG can't overcome the resistance of the first round sliding along the feed lip of the mag.
    You say the upper has 1K rounds on it, how many rounds on the lower (which would include the buffer spring)?
    I'm starting to agree with your first assessment of replacing the buffer spring, normally they have approximately a 5K life span.
    Increasing the mass of the buffer will only further impede the movement of the BCG from a static position to a dynamic one. In other words it will make it more difficult for a weak buffer spring to push a heavier buffer from a static position.
    Last edited by Hawk; April 4th, 2017 at 11:40 AM.
    Toujours prÍt

  7. #37
    Join Date
    Jul 2012
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    Hockessin, Delaware
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    Default Re: AR Failure to Feed - Please Read

    Quote Originally Posted by Hawk View Post
    It has to be a combination of the bolt carrier group spring tension and the mag's spring tension on the rounds. The BCG can't overcome the resistance of the first round sliding along the feed lip of the mag.
    You say the upper has 1K rounds on it, how many rounds on the lower (which would include the buffer spring)?
    I'm starting to agree with your first assessment of replacing the buffer spring, normally they have approximately a 5K life span.
    Increasing the mass of the buffer will only further impede the movement of the BCG from a static position to a dynamic one. In other words it will make it more difficult for a weak buffer spring to push a heavier buffer from a static position.
    I'm with Hawk here. The bolt is having trouble stripping the round out of the mag. We need to know a couple of things:

    1) What types of mags have you tried? Some GI mags are better than others. PMAGS, Lancers, D&H are all normally G2G.

    2) Do you have another buffer spring laying around? How about try keeping a mag loaded to capacity for a couple days and then try it? (Might reduce spring tension in the mag).

    3) Do the feed ramps in the barrel align perfectly with those in the receiver? Any burrs?

    4) Does the brass exhibit any scratches? Normally, with bad feeding mags, you get long, axial scratches down the body of the brass.

    To me, if the above options don't return anything, a higher k spring is necessary. However, this may introduce cycling issues when running the gun...unlikely, but possible.

    Also, pictures of everything would help diagnose.
    I'm only here for the wood c-rings.

  8. #38
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    Default Re: AR Failure to Feed - Please Read

    1k on upper and lower. Built this one AR and moved onto a .308 F Class build (I currently have listed for sale on here - go check it out)

    Planned on adding pics of this build soon - I will have a detailed report in a few days. I do not keep this gun at my house, so I need to go pick it up and tear it down.

    Truly appreciate all of the feedback guys!

  9. #39
    Join Date
    Aug 2010
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    MT JOY, Pennsylvania
    (Lancaster County)
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    Default Re: AR Failure to Feed - Please Read

    Quote Originally Posted by TetsuFury508 View Post
    Will do, I have to drive up to Butler to get it this week. Will report back with my findings later this week/weekend
    did you figure anything out?
    "I have never paid more then $10. for a Pmag"

  10. #40
    Join Date
    Jul 2017
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    South Eastern PA, Pennsylvania
    (Delaware County)
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    Default Re: AR Failure to Feed - Please Read

    Here are the areas I would check or replace (not in any specific order).


    1. try a new mag or one you know for sure that works
    2. check or replace your gas rings on the bolt - you can test this. google on how to do that
    3. the bolt O ring could need replacing. I purchased a NIB BCG from PSA and it was missing the O ring and had similar problem with feeding
    4. check or replace buffer spring and\or buffer
    5. gas tube could be dirty and need replacing - although you need a lot of rounds before that needs replacing
    6. If you have another BCG try that to rule other lower issues, ammo etc


    lots of good suggestions from other members- good luck

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