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Posted: 2/7/2006 6:12:20 PM EDT
[Last Edit: 3/9/2006 1:38:48 PM EDT by -RotorDemon-]
Don't know what the hell is going on with this thing.. I try to insert any of my 20 mags and they won't lock unless the carrier is pulled as far back as possible, drop the charging handle and it loads as normal, Fire, ejects the case, and the carrier gets hung up, pull the charging handle back and let it fly, Loads, fires.. Continued.

I'm no AR guru but I think the carrier is blocking the mag from seating in the mag well, I see no abnormal wear on the carrier/bolt. This first started happening at the January Shoot. and today it was so retarded I just put it away in embarrassment.

I stripped it there, tore it down, made sure everything was in the appropriate place / position, re-assembled and same ol crap.

WTF?!

Edit: I think I narrowed it down to the carrier. But I don't want to put a bazillion dollars down just to prove myself wrong, Since the original bolt/carrier has around 1500 rounds through it and was cleaned after every shoot.
Link Posted: 2/7/2006 6:18:10 PM EDT
Link Posted: 2/7/2006 6:43:05 PM EDT
[Last Edit: 2/7/2006 6:45:12 PM EDT by -RotorDemon-]
When the rifle was working properly, it ran every mag flawlessly.

I haven't tried them in another rifle, the problem has to lay within this one. AFAIK themag catch is working properly. with the upper off of the rifle.. they insert, lock and drop free as they should.

Edit: 500 posts.
Link Posted: 2/7/2006 6:47:55 PM EDT
Bad mags will do that.
Link Posted: 2/7/2006 6:50:07 PM EDT
[Last Edit: 2/7/2006 6:51:36 PM EDT by -RotorDemon-]
But 20 of them?????

Edit: 21, I just opened a new USGI out of the wrapper and I can't get it to lock with the upper on.
Link Posted: 2/7/2006 6:50:50 PM EDT
Link Posted: 2/7/2006 6:58:26 PM EDT
Link Posted: 2/7/2006 7:05:22 PM EDT
yeah - check the bolt stop.

Shot gun the upper and push the bolt stop. does it move freely? good spring? not binding? Not broken, bent, chewed up, siezed in place?

You haven't been dryfiring just the lower have you? w/ out the bolt in the way the hammer will impact the bolt stop and break it.

Link Posted: 2/7/2006 7:35:04 PM EDT

Originally Posted By GackMan:
yeah - check the bolt stop.

Shot gun the upper and push the bolt stop. does it move freely? good spring? not binding? Not broken, bent, chewed up, siezed in place?

You haven't been dryfiring just the lower have you? w/ out the bolt in the way the hammer will impact the bolt stop and break it.




Bolt stop is functioning fine, and no I have not dry fired with the lower seperated. But on top of the bolt catch theres a pretty decent sized brass scratch on it.

Link Posted: 2/7/2006 7:35:13 PM EDT
[Last Edit: 2/7/2006 7:39:00 PM EDT by Hoppy]
It may be the mag catch is worn or dirty and the 20 rounders have a slightly different mag slot than the 30 rounders. Seperate the upper from the lower and insert both the twenty and thirty round mags noting the slop while pushing up and pulling down on the mag.


ETA: After looking at the picture I'd make sure the bolt stop is working freely and stays down with the follower lowered. The spring may be broken too.
Link Posted: 2/7/2006 8:06:55 PM EDT
[Last Edit: 2/7/2006 8:15:25 PM EDT by -RotorDemon-]
I'll get a punch set and take the bolt stop off. The wierd thing about it is when I cycle it slowly it almost seems like the carrier is dragging on the top of the mag, but yet there is no wear on the top of the mag.

Hmmm.. I forgot to add in the first post that when it fails to feed the following round the round is pushed into the feed ramp but then the carrier moves over the top of the round. almost like a stovepipe in a .22.

I had better stop and get some snap caps so I don't have a KB if the bolt decides to punch the primer.

Edit: I'll get a pic of what it does here in a minute.

Sorry for the blurry pic.

Link Posted: 2/7/2006 9:16:52 PM EDT
Link Posted: 2/7/2006 11:19:38 PM EDT

Originally Posted By petagunner:
Hows the key on the carrier? If it came loose, wouldn't it allow the bolt to ride up like that?

Either way, I feel it's narrowed to the bolt stop, mag catch or the carrier now. Keep at it, I'm sure you'll find it and the light will come on



good idea with the bolt key. is it a bushmaster?
Link Posted: 2/8/2006 12:10:55 AM EDT
Yeah.. the upper is a Bushy.
Lower is a DPMS
Link Posted: 2/8/2006 4:08:34 AM EDT
[Last Edit: 2/9/2006 1:54:59 AM EDT by TheRealKiller]
MR.Demon is saying any one of his 20 mags not one of his 20 round mags.


My .02 is that your spring in the mag catch is broken and or bitched up. carrier key or bolt are something bad. did you get a good look at the bottom side of your bolt the big brass mark on the bolt stop makes me go huh. maybe it is missing part of the lug so it isnt picking up rounds like it should. Hard to say take some more pictures of the bolt/carrier magwell/catch inside out side etc. Good luck


Link Posted: 2/8/2006 4:17:49 PM EDT

Originally Posted By TheRealKiller:
MR.Demon is saying any one of his 20 mags not one of his 20 round mags.





Damn! I'm gonna have to start reading with both eyes.

I'd still look at the mag catch and bolt stop. If the mag catch is allowing the mags to be too high it may hinder the bolt travel as well as push the bolt stop up.

or not.
Link Posted: 2/8/2006 8:17:17 PM EDT
First questions to ask:

  1. Did you completely describe the problem? (See below for examples.)

  2. What did you change, or what happened to the rifle since just before the January match?

The cycle of operations, and where failures occur in said cycle can be used as a troubleshooting guide. See www.armalite.com/library/techNotes/tnote50.htm.

Anything that slows the bolt down (hammer drag, fouled upper, mainspring or buffer drag, or a sticky bolt stop) can cause a short cycle, resulting in the bolt-over-base feed failures you're seeing.

  1. Does the failure to lock the mags occur only with full mags or with empty/partially empty ones as well? If it's the former, your magazines are too full. If it's the latter, your magazines are sitting too high in the receiver - file down the top of the magazine catch. OR you may have bent your upper. As crazy as it sounds, it's possible. Looking at an AR, the only thing that keeps the magazines from sliding further up into the lower receiver are two "lips" milled into the upper receiver. If the receiver is bent so the barrel points left, right, or above the original centerline of the upper, the magazine runs into one or more of the lips sooner - and the bolt carrier hangs up as it tries to take the bend. It takes a fair amount of force to do this, but the weight of a really fat barrel, too many accessories hanging off the front end, or too hard a fall can "spring" an upper.

  2. Sometimes, a dirty mag catch (dirt wedged between catch and receiver) sticks. Yours may be sticking somewhere between fully up and fully down. This explains the slow cycle, but not why your magazines don't latch.

  3. The dragging feeling may be coming from the carrier interacting with the hammer. Check underneath the hammer and trigger mechanism to see if something (i.e., primer) isn't wedged underneath.

  4. Check the buffer, buffer tube, and spring. Give 'em a good cleaning if needed.. A weak spring, or dirty spring or buffer can cause drag, causing the rifle to short cycle.

  5. Cold weather can also be a culprit. Oils and greases are more viscous, resulting in slower cycling. Cold weather also causes metal to contract, with aluminum shrinking more than steel. Your magazine may effectively ride higher in the lower, and the bolt carrier rides lower. Also, the fit between upper and bolt carrier is tighter. Thoroughly degrease the rifle, then run it dry, or with a light coat of lubricant.


If all else fails, it never hurts to go back to the manual. AR15.com Copy of M16 Operator's Manual
Link Posted: 2/9/2006 2:16:46 AM EDT

Originally Posted By Asa:

  • Cold weather can also be a culprit. Oils and greases are more viscous, resulting in slower cycling. Cold weather also causes metal to contract, with aluminum shrinking more than steel. Your magazine may effectively ride higher in the lower, and the bolt carrier rides lower. Also, the fit between upper and bolt carrier is tighter. Thoroughly degrease the rifle, then run it dry, or with a light coat of lubricant.





  • THAT could very well be it.. Nothing was changed before the january shoot. and watching the mag it does ride very high. probably 30lbs of pressure will get the mag to latch and it is SOLID. I tore it all down today, everything minus the barrel, forward assist, dust cover and the bolt hold open.

    the last time I shot it before the jan shoot, the weather was in the 70's and it functioned great. I ran 600 rounds through it in seperate mags.

    I'll take it out next week, hopefully warmer.

    THANKS for the info and the links!
    Link Posted: 2/10/2006 8:48:28 AM EDT
    I'll be the first to say it......................................................Get an AK!
    Link Posted: 2/10/2006 10:35:35 AM EDT

    Originally Posted By Real_estate_salesman:
    I'll be the first to say it......................................................Get an AK!



    I own a Saiga in x39 So.. I kinda do. It has never failed to fire on me.
    Link Posted: 3/9/2006 2:49:54 PM EDT
    IM sent
    Link Posted: 3/9/2006 4:02:06 PM EDT

    Originally Posted By dabigbozman:
    IM sent



    Replied!
    Link Posted: 3/9/2006 4:11:01 PM EDT

    What kind of buffer are you using and what kind of FSB?

    Yes, they can cause problems in the cold but work fine in the summer heat. Short stroking with XM885 is a serious problem because that is powerful ammo.
    Link Posted: 3/9/2006 5:57:58 PM EDT
    The FSB is the stock Bushmaster (Like I said I'm not a know it all)

    As for the stock buffer(s) I have a Tapco 6 position and the DPMS A2 stock

    The A2 stock (spring and buffer) functioned flawlessly, Bumpfire and all
    The Tapco stock (spring and buffer) functioned alright, no problems with loading, cycling, it didn't bumpfire as well.

    They worked fine before this problem. I've swapped all the crap back and forth. no fix.

    I'm damed sure that when I find the problem with why the mags dont like to lock without excessive force (not with a hammer ) then that would be the source of my problems.
    Link Posted: 3/9/2006 6:53:32 PM EDT
    The picture of the scratch looks like a bolt lug is dragging low. Have you pulled the bolt to verify it is not cracked?
    Link Posted: 3/9/2006 7:23:42 PM EDT
    Wait.. I think I found something


    *crosses fingers*
    Link Posted: 3/9/2006 7:53:14 PM EDT

    Originally Posted By -RotorDemon-:
    Wait.. I think I found something


    *crosses fingers*



    well, anything
    Link Posted: 3/9/2006 8:03:43 PM EDT
    Hmm.. nope it's still hard to lock a mag in but I was doing some last minute cleaning in and I think it's called the "Carrier Key?" had a semi loose bolt, so I removed it and cleaned the excess carbon off torqued it back down and peened it.




    could it be bent upwards thus forcing the carrier down?
    Link Posted: 3/9/2006 8:05:26 PM EDT
    Link Posted: 3/9/2006 8:11:16 PM EDT
    [Last Edit: 3/9/2006 8:12:23 PM EDT by -RotorDemon-]

    Originally Posted By petagunner:

    Originally Posted By petagunner:
    Hows the key on the carrier? If it came loose, wouldn't it allow the bolt to ride up like that?




    Told ya so??????? Hope that's it!!!!



    Still way to hard to put a loaded mag in. Unloaded ones lock as they should.

    BUT. I think it's a good start, with gas leaking around the key (Noted carbon buildup around it) I bet that can cause short strokes and FTF's
    Link Posted: 3/9/2006 9:47:34 PM EDT

    Originally Posted By -RotorDemon-:

    Originally Posted By petagunner:

    Originally Posted By petagunner:
    Hows the key on the carrier? If it came loose, wouldn't it allow the bolt to ride up like that?




    Told ya so??????? Hope that's it!!!!



    Still way to hard to put a loaded mag in. Unloaded ones lock as they should.

    BUT. I think it's a good start, with gas leaking around the key (Noted carbon buildup around it) I bet that can cause short strokes and FTF's



    and it is a bushmaster... shocked. just shocked.
    Link Posted: 3/10/2006 5:39:00 AM EDT

    Originally Posted By GackMan:
    and it is a bushmaster... shocked. just shocked.





    Link Posted: 3/10/2006 8:10:33 AM EDT

    Originally Posted By -RotorDemon-:

    Still way to hard to put a loaded mag in. Unloaded ones lock as they should.




    Perhaps you should try it with a Colt bolt carrier.
    Link Posted: 3/10/2006 8:17:32 AM EDT
    LOL Yes, deff switch to Colt.
    Link Posted: 3/10/2006 8:25:57 AM EDT

    Originally Posted By TangoFoxtrot:
    The picture of the scratch looks like a bolt lug is dragging low. Have you pulled the bolt to verify it is not cracked?



    That is a good point TF. The angle of the scratch looks like the bolt head was turning while making that mark.

    Does the bolt move in and out smoothly when out of the carbine?

    CH
    Link Posted: 3/10/2006 9:36:39 AM EDT
    [Last Edit: 3/10/2006 9:38:20 AM EDT by ch139]
    Couold your DPMS lower be out of spec? Location of mag catch a bit too low?

    ETA: If you're around the Salem or Albany/Corvallis area I'd be happy to let you install all your stuff onto one of my complete lowers.
    Link Posted: 3/10/2006 10:23:39 AM EDT

    Originally Posted By -RotorDemon-:

    Originally Posted By GackMan:
    yeah - check the bolt stop.

    Shot gun the upper and push the bolt stop. does it move freely? good spring? not binding? Not broken, bent, chewed up, siezed in place?

    You haven't been dryfiring just the lower have you? w/ out the bolt in the way the hammer will impact the bolt stop and break it.




    Bolt stop is functioning fine, and no I have not dry fired with the lower seperated. But on top of the bolt catch theres a pretty decent sized brass scratch on it.

    x11.putfile.com/2/3722332624.jpg



    Just thought I should mention:

    That scratch mark is absolutely normal.
    Look carefully at the bolt catch -- its wedge shaped, with the taper starting from towards the barrel, and the sharp edge back towards the stock.

    When the last round is fired, the magazine follower pops up and presses on the protrusion on the bolt catch, lifting it up. When the bolt tries to go forwards after its recoil, the face catches on the flat face at the rear of the bolt catch.

    Now, having loaded the last round into the chamber, the follower is up, pushing the bolt catch up to its locking position. So, if its going to catch the bolt, it has to be higher than the bolt ... which means that it is going to have to be pushed down for the bolt to pass over it on the recoil.

    That is whay its wedge shaped. The bolt pushes it down as it comes back, once the bolt is passed it pops back up to catch the bolt on its way back forwards.

    If you doubt me, put an empty magazine into your AR and slowly pull the charging handle back. You will see the bolt head push the bolt catch down as it passes back over it.

    That is what causes the scratch.

    It seems that not all bolt catches are created equal, some are made of harder material, and some have harder parkerizing, so some show up the scratch more than others.

    Don't worry about this mark -- other than to let it remind you that you should lubricate the top of the bolt catch from time to time.
    Link Posted: 3/11/2006 4:10:27 PM EDT
    Welp.. Got back after PR, and would like to thank everyone for all of the information, help and assistance.

    The AR worked flawlessly today!
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