AR 10 cycle issue

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  • cobra

    Ultimate Member
    Feb 26, 2009
    2,058
    White Marsh
    I have a 2 year old new Bushmaster hunter ar 10
    Shot it for first time this past week.( yea I know bought too many toys back in 2013 just now getting around to shooting it)
    Accuracy is good but can stand a trigger upgrade.

    Problem is when using 10,20 round mags don,t have any 5 rounders, it cycles fine till last 4 rounds (new magpol mags) it wants to load new round before spent casing is completely elected out of barrel,not guite a stove bolt but new round jams spent round in barrel. Happens with multiple new mags.

    My thought is it might be overpassed?
    Fired 120 rounds thru it with same result. Understand they need break in but symptom remains
    Rifle clean and lubed.
    What should I look for in solving this problem? Factory build so unsure of buffer,spring,ect. Used
    Thanks for the help
     

    firemn260

    Active Member
    Sep 15, 2015
    354
    Harford County
    I’m not a expert and I’m sure someone who knows more than me will be along shortly but it seems to me that a lot of 308 AR platforms are severely over gassed. I was helping a friend of mine figure out a psa 10 that was doing the same thing about every 5 rounds or so especially with the last few rounds in the mag. With his suppressor on it, forget about it. Cases where ending up stuck backwards and everything. I switched out his block for a slr adjustable, tuned it for the least amount of gas needed to lock the bolt back on a empty mag and hasn’t had a issue since.

    I can only give you my best guess as to what was happening and I could be totally wrong. The weapon being over gassed is causing the extractor to lose its hold on the spent casing on its way rearward causing it to stay in the ejection port. Only thing I can think of in your situation if this is the case is the resistance on the bcg from a full magazine is enough to slow it down enough to not to overcome the extractor. The last few rounds in the mag creates less resistance on the bcg to the point where it will outrun the spent case jamming the weapon.

    Again This is just my opinion based on what I have learned about this platform over the years. I could have it all wrong though. I’m sure better advice will be along shortly. Good luck with it.
     

    mac1_131

    MSI Executive Member
    MDS Supporter
    Jan 31, 2009
    3,280
    Any signs of pressure on the cases? Is this box ammo?

    Over pressure can cause difficult extractions which might produce same symptoms.

    Not an expert here but am an AR-10 owner and those things run on the hairy edge.
     

    clandestine

    AR-15 Savant
    Oct 13, 2008
    37,031
    Elkton, MD
    Use different mags. Magpul .308 mags are not that great to troubleshoot with. Use Lancers if you can.

    Beyond that it's hard to diagnose without seeing it.

    Sometimes it's minor things like extractor or ejector tension. Sometimes the ejection port needs to be relieved on the front. Sometimes they need adjustable gas.
     

    ras_oscar

    Ultimate Member
    Apr 23, 2014
    1,666
    When I first started using my Anderson AR 10 I had all kinds of feeding problems. Turned out I was resting the rifle on the mag. The top lips were slowing down the bolt to the point I got a couple stovepipes. However, my problemns were not limited to the last 4 rounds. Perhaps you have a weak mag spring?
     

    Wuntsum

    Member
    Sep 20, 2018
    85
    I think firemn260 is in the right path. I had a week extractor spring myself which was causing similar issues. I changed it and it solved my problems. And over gassing could cause the same symptoms. Sometimes new weapons need a break in period because meshing surfaces are so tight or have birs that need to be smoothed down. Even some new weapons have bad Springs so give them a check. Also a heavier buffer would slow your bolt carrier group down and might help with the problem.
     

    cobra

    Ultimate Member
    Feb 26, 2009
    2,058
    White Marsh
    Great ideas. Thanks for the comments.
    Different ammo has been tried,same result.
    multible mags( all new) have been tried but all same brand magpol,will try to borrow different brand at range and report.
    I will clean rifle again,paying attention to ejector,maybe just replace spring.
    Will also look for unusual wear on bolt carrier and ejection port although it does throw spent cases fine when working. I’ll color any shiny spots on ejection port with black marker to see where good shells hit when they eject to give more info.
    Can anyone recommend a buffer and or spring.

    Really like the rifle even know it has a “bit” of a kick with hard plastic stock on it compared to my ar 15’s, it’s still fun and think it will be very accurate once trigger upgrade is done.
    Off bi pod and sand bag will shoot 1+1/2 groups but stiff hard trigger is hindering me.
    Thanks all
     

    Clifjr

    Active Member
    Feb 2, 2014
    966
    Germantown
    I have a newish DPMS AR10 that I got a few years ago and while I haven’t had any problems with it, I had read about problems like this for all AR10’s. I went with info I found here at MDS and got a Tubb flat wire buffer spring http://www.davidtubb.com/bufferspring-sr-ar10 and also got a heavy buffer from Kak industries https://www.kakindustry.com/lr308-carbine-buffer-heavy that my brother suggested and it really made a difference in what recoil I had felt and the action just seems smoother to me. Adjustable gas block and a muzzle brake is in the future also.
     

    cobra

    Ultimate Member
    Feb 26, 2009
    2,058
    White Marsh
    So it’s been a few months and I’m going to dust off the problem ar 10 and shoot it again up my “personal property/range up WV when I open cabin in April. Since last time cleaned and polished chamber. Put new extractor spring in it. I want to install adjustable gas block on it before I go to at least eliminate over under gassing as a cause.
    What is a recommended adjustable gas block. Barrel is fluted with no pined sight
    Rather factory bushmaster gas block is secured with Allen screw so “should” be easy swap.
    What to you all recommend?
    Thanks
     

    slsc98

    Ultimate Member
    May 24, 2012
    6,746
    Escaped MD-stan to WNC Smokies
    ... it wants to load new round before spent casing is completely elected out of barrel,not guite a stove bolt but new round jams spent round in barrel.
    ...

    Hey Cobra, you describe THE EXACT choking I experienced with my DPMS G-II MOE - a 3-Gun buddy and his wife who run G-II Recons told me ditch the MagPul DPMS ships with their guns* and go with Lancer L7 AR-10 .308/7.62x51mm Advanced Warfighter Magazines.

    Immediately end-of-any issues for me or the rifle since I switched to the Lancer mags. They are pricey but, the wife and kids ALWAYS know what they can get me when they need a gift idea for any occasion, ha-ha!

    *(I think it was on arfcom where a poster said he contacted DPMS about problems with the MagPuls they ship with their rifles and the rep. told him, “You need to buy one of our (DPMS) mags.” Obviously, this is all hearsay but, if that poster / post was accurate I cannot fathom why DPMS wouldn’t just ship “their” mag with their rifles.

    Oh well, chalk it up to conjecture on my part I guess.

    Except the tip on the Lancers!

    Best o’ Success!

    (And, ha-ha, my G-II was a 2016 I didn’t get around to shooting until just last year!!! :-O
     

    cobra

    Ultimate Member
    Feb 26, 2009
    2,058
    White Marsh
    Thanks
    Your the second poster that recommended Lancer mags
    I will get a few to try and see how rifle performs before adding gas block as a baseline for testing.
    At least that might help others with same problem before I swap gas block.
    I would be surprised if bushmaster and magbuls mags were the problem and Lancer mags solved the problem.

    Will still try to tune rifle so it shoots other mag brands in the end.
    Thanks
     

    cobra

    Ultimate Member
    Feb 26, 2009
    2,058
    White Marsh
    From advice given so far on possible cause’s.

    Just received a Superlative adjustable gas block and new heavy buffer along with a 10 round Lancer mag. In hopes of solving problem. No new bolt or ejector upgrades.

    My guestion is keeping in mind this is a factory build bushmaster rifle. When going thru rifle, the ejector has a spring only,not spring and o ring. Is this correct ?

    I plan on trouble shooting rifles problem first week in April up my property in W V in April but want to be sure everything is stock before I start making changes
    Adding parts.
    Goal is to make one change at a time to find cause of problem rather then add a bunch of new parts,find out it works but not know what solved original problem.
    Thanks
    I’m still thinking gun is slightly overpassed.
     

    cobra

    Ultimate Member
    Feb 26, 2009
    2,058
    White Marsh
    Sorry this is an old thread but wanted to update since I finally got a chance to shoot rifle since I discovered problem.
    Since last session installed adjustable gas block along with a few lancer mags.

    Tweaked gas block loading One round at a time till bolt locked back.
    Loaded 10 round mag pull and lancer mags. Both shot fine till last 2 rounds where I could see where spent shell had “dent” in front of casing as if new round was still loading before spent casing was ejected. ( reason I thought it was over gassed and cycling too fast)
    At this point loaded a round at a time a found 1 out of 3-4 where ejector would not hold onto round to pull out of chamber and eject.
    No signs of case being ripped off, no markings on sides of case as if stuck in barrels.
    At this stage seems the extractor may be the issue.

    Stock bushmaster rifle and bcg.
    Question is upgrade ejector spring? Do O ring mod? Replace ejector?
    Thanks
     

    KIBarrister

    Opinionated Libertarian
    MDS Supporter
    Apr 10, 2013
    3,923
    Kent Island/Centreville
    Sorry this is an old thread but wanted to update since I finally got a chance to shoot rifle since I discovered problem.
    Since last session installed adjustable gas block along with a few lancer mags.

    Tweaked gas block loading One round at a time till bolt locked back.
    Loaded 10 round mag pull and lancer mags. Both shot fine till last 2 rounds where I could see where spent shell had “dent” in front of casing as if new round was still loading before spent casing was ejected. ( reason I thought it was over gassed and cycling too fast)
    At this point loaded a round at a time a found 1 out of 3-4 where ejector would not hold onto round to pull out of chamber and eject.
    No signs of case being ripped off, no markings on sides of case as if stuck in barrels.
    At this stage seems the extractor may be the issue.

    Stock bushmaster rifle and bcg.
    Question is upgrade ejector spring? Do O ring mod? Replace ejector?
    Thanks

    Any pressure signs on the primers? I upgraded to a Rubber City high pressure bolt/firing pin and it helped problems such as you describe substantially (just the bolt w/ ejector & extractor, not the whole carrier)
     

    erwos

    The Hebrew Hammer
    MDS Supporter
    Mar 25, 2009
    13,866
    Rockville, MD
    Definitely sounds like a good time for an extractor and extractor spring replacement. You can get some weird failures if your extractor isn't holding cartridge.
     

    lazarus

    Ultimate Member
    Jun 23, 2015
    13,678
    Could this be an ejector problem?
    Too much spring?

    That was primarily my issue. I went AGB and that helped, but I was still getting double feeds (cartridge bouncing back in to the chamber), but at about half the rate. Replaced the ejector spring, the Brownell's one was a good 3 coils longer than the replacement I got. Still getting double feeds, but by still, I mean I got 1 double feed on a Wolf steel cased round out of 20 rounds of wolf, 5 rounds of 165gr PPU HPBT and 10 rounds of Aguila M80.

    The trip before replacing the ejector spring I got 1 double feed with wolf, 1 with the PPU 165gr and 2 with Aguila out of 20 wolf, 5 PPU and 20 Aguila.

    First trip with non-AGB and the Brownell's ejector spring I had 3 doubles with Wolf, 3 with the PPU and 4 with the Aguila (I shot 20 wolf, 10 PPU and 15 aguila that first trip out).

    Pretty sure putting a bumper on my shell deflector will solve the last of that double feed issue.

    Did make a noticeable difference. Before swapping the ejector, the moment the shell clears the port hand cycling the case just rips off the extractor and goes flying. Post it still ejects with decent authority, but way less violently (and a perk, the casing has fewer scratches on it from ejection/loading).
     

    cobra

    Ultimate Member
    Feb 26, 2009
    2,058
    White Marsh
    at this point thinking the ejector spring?

    No signs of case rim being ripped by ejector spring

    No marks on case like it's stuck in chamber

    Only happens on last round.

    Loaded a single round and it would duplicate problem 3 out of 4 times.

    Issue got much better once I slowed action down with adjustable gas block.
    If I tried to close gas block more bolt would not hold open on last round.

    This is what I leads me to think ejector spring or ejector itself problem.
    Had bcg apart several times and found nothing.

    Adding adjustable gas block and slowing down cycling was a huge improvement. Gas hole in barrel was a few thousands over sized compared to what I researched. Again factory built bushmaster which I have several and all dead nuts reliable till this one.
     

    lazarus

    Ultimate Member
    Jun 23, 2015
    13,678
    at this point thinking the ejector spring?

    No signs of case rim being ripped by ejector spring

    No marks on case like it's stuck in chamber

    Only happens on last round.

    Loaded a single round and it would duplicate problem 3 out of 4 times.

    Issue got much better once I slowed action down with adjustable gas block.
    If I tried to close gas block more bolt would not hold open on last round.

    This is what I leads me to think ejector spring or ejector itself problem.
    Had bcg apart several times and found nothing.

    Adding adjustable gas block and slowing down cycling was a huge improvement. Gas hole in barrel was a few thousands over sized compared to what I researched. Again factory built bushmaster which I have several and all dead nuts reliable till this one.

    FYI, I got this from Primary arms. Worked great. As I mentioned, a couple coils (2 or 3) shorter than the Brownell's one in my bolt.

    Sprinco AR-10 / AR-308 Enhanced Ejector Spring

    I basically did this https://www.youtube.com/watch?v=C9YMSWXVnck

    I got an inexpensive pipe clamp as I had some 1/2" pipe laying around. Didn't want to spend $50+ on a jig for what might be a one time job. Didn't cut a case down, but doing so would have made it slightly more stable. Easy enough to do. A bit tricky, but not some 4 handed operation. 2.5 hands at most.
     

    cobra

    Ultimate Member
    Feb 26, 2009
    2,058
    White Marsh
    To circle back around. After adding adjustable gas block most all issues stoped except for occasional last round failure to eject.
    Changed our ejector spring, rifle cycles fine.
    One thing noticed is slowing action down via gas block definetlly made for a softer shooting rifle
    Thanks for all those that helped
     

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