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Posted: 9/7/2009 9:20:22 PM EDT
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OK... This is a bit of a followup to the AR kaboom.... I finally saw the case and it looks like the case head separated and blew out a corner of it. From what I've read, it's from overworking the brass. Is this accurate?
When resizing, is it better to do a full length, or just the neck? -P |
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OK... This is a bit of a followup to the AR kaboom.... I finally saw the case and it looks like the case head separated and blew out a corner of it. From what I've read, it's from overworking the brass. Is this accurate? When resizing, is it better to do a full length, or just the neck? -P Sir, I agree with Mr. We-rborg, I interpret "a corner of it" to mean the failure occured on one side of the brass. FWIW, I haven't read anything about an "AR kaboom". Most case head seperations that I have seen occur near the case base in the area referred to as the web where the case wall transitions into the base and the wall thickness begins to increase. Usually the entire case head gets ejected somewhere and the body of the case gets stuck inside the rifle chamber. It's possible the failure was due to "overworking of the brass" but without more info difficult to say. JMHO, 7zero1. |
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Sir, I agree with Mr. We-rborg, I interpret "a corner of it" to mean the failure occured on one side of the brass. FWIW, I haven't read anything about an "AR kaboom". Most case head seperations that I have seen occur near the case base in the area referred to as the web where the case wall transitions into the base and the wall thickness begins to increase. Usually the entire case head gets ejected somewhere and the body of the case gets stuck inside the rifle chamber. It's possible the failure was due to "overworking of the brass" but without more info difficult to say. JMHO, 7zero1. Actually I think you are describing a case head failure and the extractor is ripping the head off. I believe a case head separation occurs higher up on the case body and is due to the brass being overworked. |
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Sir, I agree with Mr. We-rborg, I interpret "a corner of it" to mean the failure occured on one side of the brass. FWIW, I haven't read anything about an "AR kaboom". Most case head seperations that I have seen occur near the case base in the area referred to as the web where the case wall transitions into the base and the wall thickness begins to increase. Usually the entire case head gets ejected somewhere and the body of the case gets stuck inside the rifle chamber. It's possible the failure was due to "overworking of the brass" but without more info difficult to say. JMHO, 7zero1. Actually I think you are describing a case head failure and the extractor is ripping the head off. I believe a case head separation occurs higher up on the case body and is due to the brass being overworked. Sir, WADR what I tried to describe in my first post was case head seperations that I have experienced on more than one occasion. With a .308 Winchester cartridge using LC Match brass the actual line of departure occurred about one quarter inch up the case wall measured from the base of the case above the knurled line around the case perimeter. Case failures that I have experienced due to the extractor involved the extractor actually ripping a portion of the case rim off in the location that the extractor contacts the case rim. In my experience the case rim will fail before the case head will seperate. The case wall has to be pretty thin before the case head will fail and seperate from the case wall. When this occurs the actual line of departure during a case head seperation is actually pretty clean almost like someone used a tubing cutter. I've also experienced case head seperations with .223 Rem cartridges and while the actual line of departure remains in relatively the same location as it relates to the overall case length the actual dimensions escape me. While I may agree the root cause may be due to case overworking in the instances I have experienced what the OP posted does not coincide with my experiences. That's why I tried to make a distinction. Sometimes my choice of words fail to adequately describe the detail I'm trying to convey. HTH, 7zero1. |
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Where was the split, that determines if it was a case separation or a case head failure,, they're not the same. when you say corner of the head, was it near the extractor groove? 'Borg From what I saw, it looked like the case head got shifted around on the brass. As far as the corner of the head that is missing, I wasn't able to see where the extractor was relative to the missing piece. -P |
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Sir, WADR what I tried to describe in my first post was case head seperations that I have experienced on more than one occasion. With a .308 Winchester cartridge using LC Match brass the actual line of departure occurred about one quarter inch up the case wall measured from the base of the case above the knurled line around the case perimeter. Case failures that I have experienced due to the extractor involved the extractor actually ripping a portion of the case rim off in the location that the extractor contacts the case rim. In my experience the case rim will fail before the case head will seperate. The case wall has to be pretty thin before the case head will fail and seperate from the case wall. When this occurs the actual line of departure during a case head seperation is actually pretty clean almost like someone used a tubing cutter. I've also experienced case head seperations with .223 Rem cartridges and while the actual line of departure remains in relatively the same location as it relates to the overall case length the actual dimensions escape me. While I may agree the root cause may be due to case overworking in the instances I have experienced what the OP posted does not coincide with my experiences. That's why I tried to make a distinction. Sometimes my choice of words fail to adequately describe the detail I'm trying to convey. HTH, 7zero1. No worries as I was probably not explaining it correctly either. Like you, I have not seen what the OP describes. I do tend to see incipient case head separation more on 308 brass than 223 but I just recently tossed a LC case that I had fired numerous times. The line was very visible even on the outside of the case like you describe and using a paper clip I could feel a very definite ridge on the inside of the case. My AR10 beats the crap out of brass so I have seen blowouts on those but usually there is only a visible cut about a third around the case with soot from the powder. |
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The top case is a "standard" AR case seperation, the second case seperated on the first shot due to VERY thin walls. The third case is a bolt gun case seperation. The forth and fifth cases are case head failures.
'Borg 
(hope this works) OK, what the hell am I doing wrong? |
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Great photo Mr. W-rB! It is also a good illustration of the definition of separation and structural failure of the case head, and the differences.
The separations that occur during peak chamber pressure, do not show much gas leakage, except the one just at the web. Of course, that is because the brass is still sealed against the chamber when it occurs. The separation of the unit that started near the web shows some jetting toward the rear. That is because that fissure is at the end of the chamber. From there back, there is no chamber wall, hence no sealing. Complete separation was probably precluded by the bolt face taking all of the lengthwise force after the separation fissure started. Notice the direction of the case head failure fissures on the last two. Since there is no radial support of the case in that area, there is no backup structure (bolt head or chamber) that can preclude the fissure from continuining to open up except peak chamber pressure subsiding. Thanks. PS: The top three can stop your AR in its tracks if the forward portion of the case remains in the chamber after the rear portion is extracted. Sometimes the complete separation occurs after extraction, so the AR keeps running. The two on the bottom are the failures that can wreck your rifle. |
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