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Thread: 308 NM in the hospital

  1. #1
    Great Master Mike in tx's Avatar
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    Default 308 NM in the hospital

    Last week I took my 308 NM to the range to try different load, 66 gr of IMR 4350 over 180 Sierra RN projectile. 4th shot all creation broke loose. Stock in 3 pieces, magazine blown out, extractor collar blown off the bolt and wedged the bolt. The load is the min recommendation per Lyman's book. Sam and Tom think that either bolt failed or a burst case. It is at the gunsmith's now. He said that he has seen this before when he worked at Hill Country. I will know shortly if the receiver is OK. I have one load left and will take it apart to check the powder and projectile.

  2. #2
    NRA Distinguished Life Kirbydoc's Avatar
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    Mike, detonation possibly from a light load?

  3. #3
    Great Master Mike in tx's Avatar
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    Case holds 71 grains of IMR 4350. I weighed each load and inspected the powder column in each case. 90% plus full. We will know in a couple of days or so. Gunsmith is very competent and he graduated from CO school. I locked up a Marlin 336 maaaannnnyyy years ago with an overcharge and the receiver was not damaged. I am hoping the same for this one.

  4. #4
    Dogs Like Him versifier's Avatar
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    I have never heard of a S.E.E. from a too-light load using an extruded powder. I am under the impression that such things, rare though they may be, usually occur with ball powders. That does not mean I'm not open to education as I really don't know a whole lot about the phenomenon, if anyone does..... I am most interested in what the smith has to say and I really hope that at least the action is OK. Did you take some shots of it?
    "Stand your ground.
    Do not fire unless fired upon.
    But if they mean to have a war let it begin here."
    - Capt. Parker, Lexington Militia, April 19, 1775

  5. #5
    Great Master Mike in tx's Avatar
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    Got a call from the gun hospital. Bolt lug gone, case looks good for what it went through, the action appears to be salvagable. I am going to order a stripped bolt from Numerich to check headspace. If it works out that the action is OK then I will order the remainder of parts. The smith said that it looked like head space was a major contributor to the problem but not necessarily the only reason. He is going to do more research on it. The action did what it was suppose to do,

  6. #6
    Dogs Like Him versifier's Avatar
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    Some more thoughts:

    With no evidence in hand, all is speculation, but I am still wondering if it might have been a flaw (air bubble or inclusion) in the steel of the bolt that got gradually worse over time until it failed. I have seen three Taurus handguns fail disastrously with factory ammo and all three IMO were due to inclusions in steel slide and cylinders. It could not have been ammo all three times, especially not the slide failure. I'd be interested to see a good closeup photo of what is left of both the bolt lug (if found) and the bolt itself right at the point where the lug sheared off. We know a LOT more about metallurgy today than we did when the rifle was built.

    Was the case new, full length sized, or was it neck sized and fully obturated to the chamber? I have no experience loading belted magnum cases (or any cases with that high a pressure level), but I have a lot of experience with regular rimmed rifle cases and it occurs to me that the feeling of a good snug fit of case to chamber as the bolt normally closes would be pretty much indistinguishable to the hand from the feeling if the the chamber had slightly insufficient headspace. And I don't understand how a couple of thou excess headspace would cause an issue unless the case's shoulder was set back too far too many times by full length sizing to the point where the brass of the case body thinned to the point the head separated, common in rimmed cases like .303Brit and 7.62x54R (you neck size them and don't FL size until you absolutely have to set the shoulder back - and you give the cases a "bright ring" inspection and the wire test to check for incipient head separation every loading). I have read and always assumed as true that the same rules apply to belted cases. Am I correct?

    I'm not sure what "looked good for what it went through" actually means. Did the case fail and if so where? I think the actual location on the case where failure occurred ought to give some important clues.
    "Stand your ground.
    Do not fire unless fired upon.
    But if they mean to have a war let it begin here."
    - Capt. Parker, Lexington Militia, April 19, 1775

  7. #7
    Great Master Mike in tx's Avatar
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    The case was necked sized only. I like to feel a little resistance when I close the bolt. I try to use the choulder rather than the belt for head spacing. It seems to make the brass last longer. I will now be using the ring test EVERY time for every rifle.
    I will get pixs to you. It might have been the bolt that failed. From what I understand is the the lug was found.

  8. #8
    Great Master Mike in tx's Avatar
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    Just returned from the smith. It appears that the head space was the culprit. Tore 1/2 of one of the lugs off and dinged the rear lug in good shape. I use Numerich for parts but is any one has any other places to try, especially for a Santa Barbera Model 98, Golden Centurion, bolt and parts it would be appreciate to be informed of such. Smith said that the barrel looks good but if it needs to be set back to get another barrel but the chamber looks good.. Receiver looks good. More info on TheReloadBench on facebook

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    Dogs Like Him versifier's Avatar
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    I left the FB group a couple months back after a personal attack from an ignorant new member. Life is too short to have to deal with that kind of shit. I have neither the time nor the patience for it.
    "Stand your ground.
    Do not fire unless fired upon.
    But if they mean to have a war let it begin here."
    - Capt. Parker, Lexington Militia, April 19, 1775

  10. #10
    Great Master Mike in tx's Avatar
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    I am sorry to hear that. You were a valuable asset to the group. Newbies should be controlled. It is still a very informative group, IMHO

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check        

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