What could cause this?

Discussion in 'Advanced Gunsmithing & Engineering' started by Elite Precision, May 14, 2019.

  1. Elite Precision

    Elite Precision

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    curious as to what could cause this to happen? blew the bolt back, powder blasted the shooter, blew the bottom metal off. bullet went on target at correct aim. previous 3 shots fired from same box of ammo shot fine. rifle was cleaned thoroughly. then this round did this. Nosler factory made trophy grade ABLR 142gr. trued remi SA, bartlien barrel in 6.5 creedmoor.





    casefail.jpg
     
  2. Nightraider

    Nightraider

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    Unsupported case head?
     
  3. Elite Precision

    Elite Precision

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    as in the bolt nose recess is too deep? and the bolt nose isnt supporting the case enough?
     
  4. Coyotefurharvester

    Coyotefurharvester

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    So the round before the brass in the pic, blew the bolt open. And then the rifle was fired again, without the builder inspecting it for damage?
     
  5. Bill K

    Bill K Silver $$ Contributor

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    How did the bolt blow back, if it was closed and lugs did not shear ? The ring around that base would indicate a over load/charge. Maybe this one round somehow got extra powder when it was loaded. Just some thoughts.
     
  6. KMart

    KMart Gold $$ Contributor

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    The way I am reading your write-up is:
    3 shots fired from a box of factory ammo
    Then the rifle was thoroughly cleaned
    Then the 4th shot from the same box of ammo separated and caused damage.
    Is this correct?
     
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  7. Nightraider

    Nightraider

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    Yup or a flat face breech with too much gap. Could also be as simple as a bad case, like a case head separation type deal.
     
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  8. NZ_Fclass

    NZ_Fclass

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    bump
     
  9. Dusty Stevens

    Dusty Stevens COVFEFE- Thread Derail Crew Gold $$ Contributor

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    Thats a shoddy chambering job at best. Even a severely overpressured load wont blow down the feed ramp. Please dont shoot this rifle anymore until a qualified rifle builder corrects it. Scary stuff coming out of garages these days.
     
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  10. gunsandgunsmithing

    gunsandgunsmithing The best tuners and wind flags on the market Gold $$ Contributor

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    Hard to be sure from the pic but it does look like too much unsupported case.
     
  11. hoz53

    hoz53 Gold $$ Contributor

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    Didn’t leave an obstruction in the barrel did you.
     
  12. theallcineyes

    theallcineyes

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    so many variables its hard to give a definite answer. some of the more likely are, over charged load, bullet set back, bad case. my guess would be either a bad case.
     
  13. Ggmac

    Ggmac Gold $$ Contributor

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    Firing pin was stuck in the fired position , when closing bolt it fired the case WITHOUT the lugs being in battery ( fully locked ). Hope everyone is okay .

    Or the trigger didn't hold the cocking piece and it followed the bolt , again firing the case while not in battery ( fully closed).
     
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  14. Elite Precision

    Elite Precision

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    yes this is correct.
     
  15. Elite Precision

    Elite Precision

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    whats your definition of "shoddy"? whats something you recommend checking for? chamber run-out? concentricity? yah this is way scary. not sure where to start other that a complete tear down and check. thanks for your input..
     
  16. Elite Precision

    Elite Precision

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    from what i know of the situation. this wouldnt be the cause.. the shooter said he had placed bolt into battery and had plenty of time to settle crosshairs on target and execute a proper trigger press.

    thanks for your input..

    Matt
     
    Last edited: May 15, 2019
  17. Elite Precision

    Elite Precision

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    no, the shooter said the bullet exited the barrel and actually was on target accurately.
     
  18. 243winxb

    243winxb

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    Excessive chamber headspace is my guess. Caused case head separation.
     
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  19. J355

    J355

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    Pics of the previous cases would be nice, may show a bulge from a overdone feed ramp
     
  20. Elite Precision

    Elite Precision

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    i tore apart the barreled action and checked to make sure everything was still intact internally. the bolt lugs, bolt face, extractor, ejector, firing pin are all fine. the bolt face did have a huge over pressure sign of the entire case end imprinted on it with legible writing! ( ive never seen that before) the internal lug abutments are fine, not cracked or sheared or missing a corner. i did get the first three fired nosler rounds, and a previously shot 20 rnd box of ammo that was shot from this rifle that was all of the initial break in rounds used. the first box of 20 was hornady match 140s. all fired brass looked fine. there were a couple of the hornady brass that had a real faint horizontal line scratched into it on half of the circumference that matches up to the blow out line of the nosler brass pictured. the 3 other fired nosler brass showed a more distinct scratch mark, and it was more prevalent than on the hornady brass. i took 1 round of the nosler ammo and fired it out of a factory remington aac-sd that i have, and there was no mark.

    i ran a go/no go gauge thru it, and it passed fine. closed effortlessly on the go, and was locked out on the no go just as it should. i measured the action and bolt and checked those measurements on the barrel and chamber for blueprinting specs and all the measurements (tenon length, go gauge protrusion, bolt face recess) came out within -/+ .0001"

    I chucked the barrel up in my lathe and dialed it in to .00015" of true. checked the chamber run out from throat to entry, and it is running true as well.

    im not sure what to do at this point. knowing all those measurements are as good. maybe it was an overcharged round. but why would those marks be on the brass? i checked the chamber entry for a burr, or a sharp edge that would be the thing that touches the brass there, and it was clean, had a small chamfer, and was smooth.



    is there anything else i can check for while this is apart? any other tests? someone from another forum mentioned to just set the chamber back and re-cut it myself. Thoughts?

    thanks everyone for their input! i really appreciate it. keep them coming.


    Matt.
     
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