short stroking issue

Discussion in 'AR-15 Discussion' started by Jordan B, Jul 1, 2020.

  1. Jordan B

    Jordan B New Member

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    Just posted in the introduction page, but i do have an issue maybe someone can point me in a direction with. I have an 18 inch mid length 223 wylde ballistic advantage hanson that i built recently. I have standard buffer and spring and used 5 different brands of ammo all 55gr. not one of them was able to rechamber after firing. they did eject, but did not rechamber. i have removed gas block and blew out line to make sure it wasnt blocked and put a small brush through the port. the carbon ring was centered around the port (no idea what the gas port size is on this and cant find the answer anywhere. sounds like .068-.078 and not sure best way to measure it either). gas tube lined up and sit well within the gas key. leak checked the gas key and made sure gas rings on bolt were good. If i shoot 62gr it will rechamber some of the time and 75gr rechambers no issue. I am wondering if i should be looking at maybe making gas port bigger or try out a reduced power spring to see how that does ? or what else i might look into ? thank you
     
  2. Txhillbilly

    Txhillbilly Well-Known Member

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    You need a set of pin gauges to measure the gas port size. Check with a local machine shop or gunsmith to see if they have them,or you can buy a set on Amazon for around $40. I'd measure the gas block also to make sure the port in it is bigger than the hole in the barrel.
    If it were me,I'd drill it out to .078",and then buy an adjustable gas block so you can adjust the gas pressure to make the gun cycle without over gassing.
    I run Superlative Arms adjustable gas blocks on all of my AR's because I shoot with suppressor's,but I would use one even if it wasn't suppressed because you can tune the gun with it.

    How many rounds have you fired out of the gun? If you built it,sometimes it takes quite a few rounds to break it in.
    Sometimes you just have to trace down the issue,but I'd start with the gas port size,and go from there. If that doesn't fix it,then try a lighter spring or buffer.
     
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  3. Ghost1958

    Ghost1958 Well-Known Member

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    Over gassed. That's why it will run with the heavier grain bullet but nothing lighter.
     
  4. sheepdawg

    sheepdawg Well-Known Member Supporter

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    Why did I think this was going to be about another topic? :confused: :rolleyes:
     
  5. Jordan B

    Jordan B New Member

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    I have between 100 and 150 rounds so far. thanks for the info on the pins.


     
  6. primer1

    primer1 Well-Known Member Supporter

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    Make sure it isn't a magazine or lubrication problem.
     
  7. bluez

    bluez Well-Known Member

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    Hmmmm...
    Which ammo are you using?
    Brand?
    Just curious to give me a sense of the problem.. a properly tuned AR will tolerate all ammo from full power (Lake City 62gr) to light loaded PMC Bronze 223/Tulla 55

    Possible causes:

    - Gas port too small,
    - Buffer spring too stiff, might try a carbine buffer spring instead of a rifle buffer spring.. you might be able to avoid changing gas port this way.
    - Are you using a full length gas system with that 18 inch barrel? If so some undergassing is not unusual.
    - Where does your ammo eject? on the graph below? This may tell us if perhaps a factor other than gas may be involved. I would also expect different ammo to eject a bit different.

    22671928017_8c68eccc92_bm.jpg
     
    Last edited: Jul 2, 2020
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  8. Jordan B

    Jordan B New Member

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    they were all 55 gr. i used armscor, federal premium, winchester x, hornaday frontier and opal ammo. I have a carbine buffer and buffer spring in it already. it is a mid length gas system on 18 inch barrel. ammo ejects about 5 oclock. Using 62 and heavier it comes a bit closer to 4-430 oclock


     
  9. bluez

    bluez Well-Known Member

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    Hmmmm, some expensive ammo in that list.. that I admit i very rarely, if ever, shoot.. is it mostly 223 rather than 556?
    when you say 62 gr which 62 gr is it? there are many very different loaded ones out there...
    Is it lake city XM855? the most common and also hottest 62gr?
    Any Federal XM193 55gr? (also hot)
    Which armsor did you shoot? M193? or 223?

    I am not saying the ammo is at fault ... a good rifle can digest nearly any 223/556 round and function , this is why so many factory rifles are a bit overgassed by design to account for so many commercial loads being soft......my LWRC M6A2 ejected at 3 o clock for commercial ammo and at 1:30-2 o clock for military loads.. that was with a "H" Buffer.. so it was very open...

    My Sig516 with adjustable gas set to "normal" gas would short cycle with PMC Bronze, ejection pattern 4:30-5 o clock..and some (but not all) of the economy ammo out there. But run just fine with XM193 (3:30-4 o clock)

    Again I am not saying the ammo is at fault just trying to get a handle how severe the under-gassing really is, as I dont have any experience in the ammo you listed... I shoot a lot so its never expensive ammo.

    With mid length gas on an 18 inch barrel you should have plenty of gas..
    Also that ejection pattern does mean its almost certainly a gas issue and not something more exotic.

    Off the cuff some common possible causes left:

    - size of gas port (or anything that will affect size of effective gas port like poor machining in rare instances may)
    - poor install of gas tube
    - Blocked gas tube

    Are you running a AR15 BCG or a "full auto" BCG (by itself heavy BCGs will not cause the problem.. but they certainly wont help short stroking)
     
    Last edited: Jul 2, 2020
  10. Jordan B

    Jordan B New Member

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    It was 62 grain and 75 grain hornaday black. armscor was basic 223. I am running ar15 BCG not full auto. I have stripped everything down and made sure gas block and tube were installed good and had good air flow through it. gas key didnt have any leaks.


     
  11. bluez

    bluez Well-Known Member

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    I looked up some of the ammo you shoot.
    For those were I found numbers they were all loaded a bit light.

    A properly tuned rifle should still be able to shoot w/o short stroke (or at least only by exception) with light loads... but it certainly doesnt help.

    I admit I am running out of ideas since u seem to have addressed the usual low hanging fruit suspects on your own.

    Since u are clearly not getting enough gas for some reason we can try to manage the symptoms (go with lighter spring and lighter buffer) and hotter ammo, which should make u run right.

    Or measure the gas port and consider asking the manufacturer what gas port size is supposed to be on there.

    If there is a discrepancy consider sending the barrel back for re work or a replacement.

    On this list 18 inch is not listed but still it may point you in the right direction:
    https://www.tacticalmachining.com/learn/ar-style-rifles/ar-15-gas-port-sizes.html

    PS: Here is a list of the ammo I usually shoot.. the hotter rounds are marked as such in the description. You seem to have a healthy ammo budget so PPU or Federal White Box XM193 should be covered ( if it wasnt for the current
    shortage).. still your problem should not stem from the ammo u shoot
    https://www.firearmstalk.com/threads/bluezs-big-review-of-commercial-ammo-in-ar15s.117369/
     
  12. Jordan B

    Jordan B New Member

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    I am going to try one of those reduced power springs and if that seems to help everything fire ok I may leave it for a bit, but I'll definitely revisit the gas port size and possibly change that if its not right


     
  13. Gatoragn

    Gatoragn Well-Known Member Supporter

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    The only time I had an AR short stroke on me, it was resolved by installing a heavier buffer.

    Newton's laws of motion apply 100% to this situation.
     
  14. oO_Rogue_Oo

    oO_Rogue_Oo Well-Known Member

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    A heavier buffer tends to increase dwell time (The time between firing and the bolt opening) so should help here. Coupled with a lighter spring would be even better.

    EDIT: I would also inspect the brass looking for any evidence of chamber issues. And inspect the bolt for any evidence of blow by. I would also be sure the gun was properly lubed. Personally I like to run a good grease on the bolt carrier rails. Oil everywhere else.
     
    Last edited: Jul 2, 2020
  15. Jordan B

    Jordan B New Member

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    Tried reduced buffer spring with heavier buffer today. Borrowed a friend's Odin adjustable buffer so I tried all combos from 3.7 oz to 5.8oz with both reduced and standard spring. All rounds from 55gr to 75gr would eject but the rounds lighter than 68gr would not rechamber. The 68gr to 75gr would rechamber but bolt would not lock back on empty mag.



     
  16. oO_Rogue_Oo

    oO_Rogue_Oo Well-Known Member

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    Then I would guess that either the gas rings on your bolt aren't sealing properly or the gas port on your barrel has an issue.
     
  17. Jordan B

    Jordan B New Member

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    Tried 3 different BCGs and same issue. Decided to make the gas port bigger and put adjustable gas block on. It Shot without issue after the switch and drilling and the gas block was wide open so it may not need the adjustable block. Even though it is low profile that gas block rubs on the handguard. I will change it back to the stock non adjustable gas block and do more testing tomorrow to make sure its still not over gassed, but I think i figured it out.

     
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  18. Sniper03

    Sniper03 Supporting Member Supporter

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    upload_2020-7-7_14-46-15.png
    Jordan
    Maybe this will help!
    This is a slide I use in the Armorer Schools.
    These are the gas port range sizes we used at the Armory/Factory.
    As far as gauging the Port Size. If you have a complete set of drill bits. And a set of Calipers being digital or what ever. You can measure the chuck part of the shaft on the drill bit. Not the cutting part! And on occasion, you can find a drill bit that fits close to the dimensions of a Gas Ports pictured above. Or purchase the set of gauges previously mentioned.

    For those with Gas Piston Guns the Port Size usually needs to be slightly larger than the above.
    03
     
    Last edited: Jul 13, 2020
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  19. Jordan B

    Jordan B New Member

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    Cool thanks for pic. had a weird happening, but dont know if its anything or not. Shot about 500 rounds since making the gas port bigger and all the sudden has failure to loads and the bolt not locking back. ill clean it and double check the gas block is in the right spot and shoot again to see if that makes a difference. possible it was dirty and just needed cleaned ?



     
  20. Roverhound

    Roverhound Member

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    Rifle or carbine stock?