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It may help to split one of the cases lengthwise you fired before this one that didn't explode and see if you see signs of separation or fatigue in the base.
Destructing one that didn't do it explosively may or may not shed light, but doesn't hurt anything.
Destructing one that didn't do it explosively may or may not shed light, but doesn't hurt anything.
I think pressure was WAY high, in order to deform the case head in that way. The case head and web is the strongest/thickest part of a cartridge case. The web area where this separation occurred is normally strong enough to remain intact at normal chamber pressures in a chamber with proper bolt face to tenon clearance, even though the case web isn't fully enclosed within, and supported by, the steel barrel tenon.
Looks like the case separated approximately at the face of the steel barrel tenon.
Be curious on the length of one of your normal cases, versus the length from the case mouth to the location of separation on the ruptured casing. So we can know how far forward from the bolt face / case head, this separation occurred.
I dunno the cause, but I do think the case was over-pressured. That is unless 1) the Lapua casing is completely defective regarding brass strength or, 2) there was excess clearance between the bolt face and the face of the tenon.
Looks like the case separated approximately at the face of the steel barrel tenon.
Be curious on the length of one of your normal cases, versus the length from the case mouth to the location of separation on the ruptured casing. So we can know how far forward from the bolt face / case head, this separation occurred.
I dunno the cause, but I do think the case was over-pressured. That is unless 1) the Lapua casing is completely defective regarding brass strength or, 2) there was excess clearance between the bolt face and the face of the tenon.
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Jim’s Hunt
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I'm a COW method person too
Culpeper
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I want enough resistance so that I re lube the bolt lugs every 25 rounds to keep the lugs from gauling.
Also, light fire forming loads has ruined many, many cases, I can not stress this enough.
In post #13, there is a clear picture of a fracture around the circumference inside the case, just in front of the web. This is typical of too much headspace. When fired, the shoulder/neck grips against the chamber wall, then the web of the case stretches to touch the bolt face. This affair creates a weak spot in the brass, right in front of the web.
Due to the bolt design, you see how the gases were vented out the bottom, brass flowed around the massive extractor, which tore the case head up when He pulled the case out of the bolt head.
Often when brass has to be sized to reduce the dia of the web for easy bolt close, the shoulder has to be pushed back further than you like which always ends up in case of head separations 4-5+ firings later.
Due to the bolt design, you see how the gases were vented out the bottom, brass flowed around the massive extractor, which tore the case head up when He pulled the case out of the bolt head.
Often when brass has to be sized to reduce the dia of the web for easy bolt close, the shoulder has to be pushed back further than you like which always ends up in case of head separations 4-5+ firings later.
percent.Hugnot
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Bad brass
That break looks the same as being cut with a fine tooth saw or file -no case separation caused by excessive headspace, which would be indicated by separation in front of the internal cartridge web, a strong work hardened portion. A real clean even separation in front of the extractor groove, the strongest portion of the case. Not a case separation caused by excessive head space.
My thinking is:
The smooth & precise separation was the result of a defect. Various materials, in the plastic state, show signs of failure or separation when subjected to force directed normal to the failed area, called a "stress fracture". My guess is that this failure was initiated when the case was made. The head area is work hardened and when the case was made by forming plastic state brass, a stress fracture was initiated, and the case failed later when more normally directed forces were applied, like in chambering a crush fit round to fire form the Ackley Improved brass case - a .004 or more crush fit.
Location of the brass in chamber has no effect on the subject separation as shown by imminent failure on non-separated areas, like shown in internal photos. Any exposed brass would be located away from internal high pressures near the bolt face with extractor groove exposed. The failure occured in front of the extractor groove surrounded by chamber walls.
I would guess that parts used for critical stuff, like life & limb, would be subjected to various tests like X-ray to look for any defects.
That break looks the same as being cut with a fine tooth saw or file -no case separation caused by excessive headspace, which would be indicated by separation in front of the internal cartridge web, a strong work hardened portion. A real clean even separation in front of the extractor groove, the strongest portion of the case. Not a case separation caused by excessive head space.
My thinking is:
The smooth & precise separation was the result of a defect. Various materials, in the plastic state, show signs of failure or separation when subjected to force directed normal to the failed area, called a "stress fracture". My guess is that this failure was initiated when the case was made. The head area is work hardened and when the case was made by forming plastic state brass, a stress fracture was initiated, and the case failed later when more normally directed forces were applied, like in chambering a crush fit round to fire form the Ackley Improved brass case - a .004 or more crush fit.
Location of the brass in chamber has no effect on the subject separation as shown by imminent failure on non-separated areas, like shown in internal photos. Any exposed brass would be located away from internal high pressures near the bolt face with extractor groove exposed. The failure occured in front of the extractor groove surrounded by chamber walls.
I would guess that parts used for critical stuff, like life & limb, would be subjected to various tests like X-ray to look for any defects.
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A case web stretched to the extent of complete separation doesn't explode the remaining, separated case head. Causes some gas leakage at the separation. This case head experienced detonation pressures. Case head is mangled. Unrecognizable.
Grossly excessive pressure, IMO.
Completely defective brass could always cause this alone, or could be a contributing factor.
Too large of an unsupported gap between the bolt face and tenon face could also be a contributing factor (this gap can be be measured now to rule in, or rule out, as a contributing factor).
Example of the importance of wearing safety glasses. Eye protection. Or risk loss of eyesight!
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IMO this is something that will probably never happen again, 1 bad piece of brass, a clump of powder that was messed up, bullet came apart upon ignition or something of that sort, I've torn all kinds of stuff up that should have looked like that but easy even close, I'm just glad you are ok.
My 2 Pennies
Bean
My 2 Pennies
Bean
Hugnot
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Shows imminent fracture.
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