What could cause this?

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

  1. wyop

    wyop

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    Sorry, didn't read far enough down in the thread.

    The thing that I keep looking at is how precise, even and uniform the case failure is - as tho the brass had been cut. Most case failures don't happen along that "clean" a line.

    I also am with the others here - the point at which the case failed seems to indicate a lot of the case is unsupported by the chamber. I'm curious if you could measure the following all the front features of the bolt - the distance from the bolt face to the rim/bolt nose, the depth of the nose recess in the barrel, etc, etc. It just "seems" as tho the failure line on the case is too far forward of the case head. And in a Rem 700 action, I'm unsure of how the case head portion of that cartridge could have the brass flatten outward like that, unless the bolt has been modified to have a non-Remington extractor on it.
     
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  2. Elite Precision

    Elite Precision

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    i agree with the uniformity of the scratch/cut. the bolt only has factory ejector/extractor. .
     
  3. Riesel

    Riesel Gold $$ Contributor

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    Have you run any of this fired brass, both Hornady and the three Noslers, thru a sizing die? I would be interested to know how much you have to stand on that press handle to resize one of these cases and after resizing, will it chamber?
     
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  4. RatRifle

    RatRifle

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    That was an out of battery detonation I believe. Remember the OP said: the bolt blew back and no damage to lugs.

    Jim
     
  5. Someoldguy

    Someoldguy Silver $$ Contributor

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    If the lugs are intact and undamaged, I can think of no other explanation than an out of battery discharge.

    Upon ignition, the pressure build forced the case to the chamber walls. At some point, the case failed driving the bolt rearward and causing the case damage as pictured. This also explains the unburned powder striking the shooter's face.

    As for the point of impact on the target, how far down range was the target located? 50 yds or less?
     
    Last edited: May 15, 2019
  6. paperpuncher

    paperpuncher Silver $$ Contributor

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    Does the chamber on your rifle look like this? If you look past the bolt nose counterbore there is a small step that the belt on the case should fit into. This is an image from the net and it is how I remember the magnums are supposed to look. Been a while since I have done one. I cant visualize how your case could fail like it did in the pics you provided if your chamber looks like this one. Im thinking as has been mentioned previously the counterbore is too deep leaving the case head unsupported allowing it to rupture. The fired cases that have the line are the ones that "bent and did not break" Hope this helps
    remington-700-xcr-2.jpg
     
    Last edited: May 15, 2019
  7. gme

    gme Site $$ Sponsor

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    how deep is the counterbore that accepts the bolt nose?
     
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  8. C.E.Smith043

    C.E.Smith043 Gold $$ Contributor

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    Is there any chance left over cleaning solvent was present in the chamber and caused a pressure spike?
     
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  9. Elite Precision

    Elite Precision

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    i have not ran the brass thru a die yet. but i will. they are not visually bulged or anything. they look normal. i have rechambered a few of the spent cases and they chambered fine and bolt closed.
     
  10. Elite Precision

    Elite Precision

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    it was a 100 yd target.
     
  11. Elite Precision

    Elite Precision

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    i dont have the exact measurements but i wanna say it mic'd to .157" which was also the measurement of the bolt nose to the face +.010" for clearance.
     
  12. Elite Precision

    Elite Precision

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    i called a contact at nosler, and sent him the pic, he had some ballistics lab guys look at it and they think it is the "unsupported case" issue. ill ad some pics they sent me to show what they meant.

    i think at this point im going to start from scratch as if i was to set this barrel back. re measure all the specs of the bolt and action. re cut tenon, bolt nose recess, and then rechamber it.

    hopefully someone can learn something about this and prevent any further injury to anyone.

    Please remember to always wear safety glasses when shooting! this guys face was bloody and peppered. he said the urgent care lady dug 4 big chunks of stuff out of one eye alone. eesh!

    be safe out there

    thanks to everyone for all the input ! its great to have this board to bounce ideas off one another and get a volume of different perspectives.




    20190515_124645.jpg 20190515_124544.jpg
     

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  13. RatRifle

    RatRifle

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    How did the bolt open and blow back to the stop? Did you witness this?

    Jim
     
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  14. Daveinjax

    Daveinjax Silver $$ Contributor

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    5E2831EE-8C20-44AD-A4C2-F83329678A14.jpeg You really need to measure the bolt nose clearance before you rechamber the barrel. You need to properly diagnose the problem first. I’m having a problem with the bolt blowing back. My experiences with severe over pressure is the bolt stays closed and you can’t open it not it blowing back. And yes , I’ve been behind a couple of over pressure rounds. Notice the bolt is still in battery. I’ve beaten the handle off two Remington 700’s. None opened and blew back. I haven’t seen one open and blow back on anyone else either.
     
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  15. hoz53

    hoz53 Gold $$ Contributor

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    Did the bolt actually blow back as you said in original post or was there just gas leakage?
     
  16. ebb

    ebb

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    I read where several stated that a cartridge case was welded to the bolt. I have had that experience once. And in my experience with a Remington and over pressure the case is not welded. On my gun and most I assume the case has swollen so much that it is jammed into the bolt nose. I made the mistake of taking the case lose with my hands and tore the bolt up. If I had put the bolt in the lathe and cut the case out of the bolt nose I may have been able to use the bolt with out much repair. As it was I pulled the extractor and the metal in front of the extractor groove off and the smith had to silver solder in a new piece and turn the recess back to proper diameter and install a Sako extractor.
     
  17. msalm

    msalm

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    This should be very easy to diagnose, what is the measurement from the case head to the black line where the case separated...it looks like a LOT more than your .157” clearance. Did you add a chamfer on the chamber edge...like a really big one? Either that or your doing your math wrong, like used a thicker recoil lug than you initially measured with.
     
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  18. msalm

    msalm

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    I didn’t see it mentioned, but what’s the tenon length on that barrel shank? I’m guessing it’s.020-.050” (or more) too short. Your counterbore only needs to be .152-5” deep (same as the bolt nose depth since the tenon length should be .006-.010” short of the lugs. If you added another .010” depth on the counterbore you went too far.
     
  19. carlsbad

    carlsbad Lions don't lose sleep over the opinions of sheep. Gold $$ Contributor

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    You can measure the unsupported case length on the blown out cartridge. It is now black. Like others said, it should be in the range of .150.

    Pull the barrel off and measure the unsupported length on a go gauge. It should be the same. The fact that this didn't happen for 3+ boxes of ammo tells me that is is not likely a smithing problem but more likely something unique to this trigger pull.

    The fact that the bolt blew back is suspicious. Really sounds like he forgot to push the handle down or something similar.

    Finally, if the black portion of the blown out round is in the vicinity of .150", then it points to a defective piece of brass. Nosler of course would like you to accept the unsupported case length theory so don't expect their lawyers to let them volunteer any other theory.

    -Jerry
     
  20. Dusty Stevens

    Dusty Stevens COVFEFE- Thread Derail Crew Gold $$ Contributor

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    Until the bolt handle goes down the firing pin cant go forward. So if the lugs arent locked it cant fire. Things happen fast and after the initial shock of something going wrong we cant really dissect the true sequence of events
     

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