Posted: 3/3/2018 4:50:15 PM EDT
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Just happened.
Specs. Wilson Combat upper/lower set. Christensen Arms 6.5 Grendel barrel. Jp bcq and Young bolt. I have about 40-50 rounds through this rifle with a JP bolt. This time I was setting up a new scope and going to do a bolt test with 3 bolts. The jp, a Young manufacturing, and the monster 6.5 bolt. Factory Hornady Eld 6.5 Grendel Ammo. Young Manufacturing bolt brand new failed after two rounds. Bolt ordered Jan 6, 2018, Invoice# 3759. Jp bolt in originally. Sighted in, shot the following group at 100 yds. Switched to the young bolt. Shot one, shot number two more right than it should be and then noticed the carnage. So failure occurred on the second shot. 
Other half of brass is in the chamber. Gun ejected the half brass and lodged the next round in the roof. Thoughts opinions on this. Another pic. Added left brass shot with JP bolt for the last 40-50 rounds. 
Moar. Same orientation as above 3 shots. 
Lug pic. Young MF proof. 
Case head. 
Bolt up close, should be able to zoom in good. 
Carrier cam pin area damage. 
Upper receiver damage. Raised bulge where that damage is. Carrier binds in receiver. 
Other half of brass recovered. 
Fired brass with JP bolt 1.510" 1st brass fired with Young bolt 1.509" 2nd brass fired with Young bolt 1.557". Failure round. Just for comparison. Using Hornady comparator. Fired brass specs for these bolts: JP 1.2135" Young 1.2140" Larue Factory 6.5 Grendel 1.2145" Right now I believe the bolt had begun failing after the first shot as brass is normal with normal primer strike. Second shot primer is nearly pierced and bolt begins collapsing causing the excessive expansion and tearing case in half. Also, there was no gasses from the failure introduced into the receiver. The bolt held long enough for the case to seal in the chamber, so I got lucky on that part. 3/3/18 Bolt failure, Young Manufacturing 6.5 Grendel 3/3/18 Contacted Young via email, tagged this post in email. Asked that they look it over and get back to me. 3/5/18. Made a follow up call to Young Manufacturing to verify email was received. Received but had not been looked at according to Young. 3/9/18. Zero contact with Young since. No reply to email, nothing. Thanks Bill |
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IMHO, that's not an overpressure failure, because the brass is intact all around the head.
That is a bolt material failure, most likely from improper material or most likely, improper heat treating. That bolt shattered. The case separation is likely a side effect from the bolt giving way. (Unless the 6.5 grendel does not fail the same way 5.56 does, and their bolts are inherently weak by design.... im not as well versed in 6.5g - but this is highly unlikely or bolt failure like this would be very commonplace. I have read there is more bolt thrust, and from looking at Young's bolt description they redesigned their bolt at some point saying "no more broken bolts") |
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That's impressive in a scary way. Is the case head intact? if so it's not ammo and I'd guess a meturalogical fault / failure. Beat by FAL 
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Never seen a bolt kaboom before. Are any of those pieces the lugs?
What would the bolt look like if it fired without being locked? I am trying to link the neck of the brass separating with the broken bolt but I cannot. Is the barrel nut tight? So us the primer strikes for both rounds. ETA - Sorry, I see the pic of the primer strikes. |
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Gotta be a bad bolt, never seen one blow like that Quoted:
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I have no real idea. My guess is an improperly made bolt. |
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New patent pending “Heavy Wall” bolt design. No more broken lugs. We don’t just machine out the bolt face on a standard 5.56mm bolt leaving a thin wall and weak lugs. We machine it right from the start and you use your STANDARD AR15 firing pin. The wall thickness on our bolt is .020” thicker than the competition giving more support to the lugs. As with all of our bolts we finish grind all critical diameters “After” heat treat resulting in a bolt that is true and square to the bolt face for 100% lug contact. Made from 9310 steel and heat treated to mil spec. |
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New patent pending “Heavy Wall” bolt design. No more broken lugs. We don’t just machine out the bolt face on a standard 5.56mm bolt leaving a thin wall and weak lugs. We machine it right from the start and you use your STANDARD AR15 firing pin. The wall thickness on our bolt is .020” thicker than the competition giving more support to the lugs. As with all of our bolts we finish grind all critical diameters “After” heat treat resulting in a bolt that is true and square to the bolt face for 100% lug contact. Made from 9310 steel and heat treated to mil spec. |
| Yeah well that shit disintegrated. |
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There are two different sized bolts for the Grendel. Sure that one was the proper size? Using a Type I (.264 LRB) barrel with a Type 2 Bolt will have excessive head space. |
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After I read this post I had to look away, close my eyes, and concentrate to remember how to spell metallurgical. For almost a full minute, I was genuinely unable to do so. I wasn't even sure about meteorological. It was very disorienting. |
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They over heated it grinding and lost the heat treatment Quoted:
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New patent pending “Heavy Wall” bolt design. No more broken lugs. We don’t just machine out the bolt face on a standard 5.56mm bolt leaving a thin wall and weak lugs. We machine it right from the start and you use your STANDARD AR15 firing pin. The wall thickness on our bolt is .020” thicker than the competition giving more support to the lugs. As with all of our bolts we finish grind all critical diameters “After” heat treat resulting in a bolt that is true and square to the bolt face for 100% lug contact. Made from 9310 steel and heat treated to mil spec. |
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Case head swipe. Over charged. Quoted:
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You guys see the ‘smiley’ (‘C’ indentation) on the truncated brass? Any ideas? Over charged. |
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That raised semicircle on the case head of the failed case looks like flow of brass into the ejector channel. Sign of overpressure
But usually you see it in combination with a flattened primer. Flattened primer Flattened primer with cratering around firing pin strike Flattened primer with cratering and flow into ejector channel. |
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Hydrogen embrittlement or improper heat treat notice the extractor survived though bent. Primer shows no over pressure, was head space checked after bolt switch? Edit: Looking at new pics Combo bad heat treat and improper head space. Somehow slipped through the Q.C. |
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Barrel lugs look okay still, one has a slight scuff. Not sure how to get the brass out of the chamber. https://www.brownells.com/gunsmith-tools-supplies/handgun-tools/stuck-case-removers/broken-shell-extractor-prod23311.aspx Last person I know with this issue, could not extract with this setup (in .308) , and wound up using a tap and die set to grab the case, and a wood dowel to pound it out. |