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Posted: 4/24/2013 4:45:52 PM EDT
Had an "issue" with a bolt failure.  Can anyone offer me advice on this issue.  This was in a 10"(registered semi SBR) that has approximately 1000 rounds.  Portion of bolt fractured and destroyed carrier, upper receiver and mag.  Barrel is fine.  Was firing standard M193 Ball.

Any help would be appreciated

http://i1316.photobucket.com/albums/t616/4JSFORME/IMG_3838_zps2231a42b.jpg
Link Posted: 4/24/2013 4:48:25 PM EDT
Here ya go, I thought I'd imbed this for ya.






Link Posted: 4/24/2013 4:49:53 PM EDT
R Guns bolt head?
Link Posted: 4/24/2013 4:51:53 PM EDT
I heard that during the panic and rush on parts, some inferior bolts were produced.  Was this a recent purchase?
Link Posted: 4/24/2013 4:51:57 PM EDT
wow what was you shooting again and I would be calling the company wherever that came from cause no way should that bolt do that unless its junk.
Link Posted: 4/24/2013 4:52:22 PM EDT
Ouch... No good man.
Link Posted: 4/24/2013 4:56:35 PM EDT
What brand was this and when did you get it?

Oh and sorry about your loss.
Link Posted: 4/24/2013 5:35:13 PM EDT
Interested to hear where this bolt came from...
Link Posted: 4/24/2013 6:01:19 PM EDT


Thank you for the assistance.

Link Posted: 4/24/2013 6:11:29 PM EDT
I cannot recall where this particular bolt came form.   It was purchased probably 20 years ago when I was putting together this rifle.



Bolt / carrier fragments took out the entire upper receiver as well as other asundry parts.  The lower was unscathed (and more importantly, so was I)  The fractured bolt piece kept the rest of the bolt from turning and disengaging so the carrier stayed in place.  The primer in the case was gon ans well as hte portion of the pase of the case that was not supported by the fractured bolt.



I have easily put 1000 rounds through this gun without any issues. until now.  Was firing standard M193 ball, not reloaaded.



I have assumed that it was the bolt failure, and not ammunition related.  Any differing opinions?



Thanks for all of the help / comments (and sympathy).  I'll get it going again soon.



Joe
Link Posted: 4/24/2013 6:15:37 PM EDT
[Last Edit: 4/24/2013 6:15:56 PM EDT by RJeff21]
Disregard, got beat to the punch.
Link Posted: 4/24/2013 7:47:13 PM EDT
[Last Edit: 4/24/2013 8:12:19 PM EDT by ricochet7]
Originally Posted By 4JSFORME:
Had an "issue" with a bolt failure.  Can anyone offer me advice on this issue.  This was in a 10"(registered semi SBR) that has approximately 1000 rounds.  Portion of bolt fractured and destroyed carrier, upper receiver and mag.  Barrel is fine.  Was firing standard M193 Ball.

Any help would be appreciated

http://i1316.photobucket.com/albums/t616/4JSFORME/IMG_3838_zps2231a42b.jpg



I am by no means an expert, but I'd lean towards an over-pressure round (or barrel obstruction), even if the barrel looks fine.
I know you said standard m193, but this reminds me of kabooms from bad ammo..
I believe several manufacturers have released bad rounds, and I have seen similar results to yours due to bad ammo.
All it takes is one bad round, OR  a squib followed by a round fired.
Everything was normal up till this round? What else do you remember about the rounds leading up to this "failure".
I'm not faulting you at all, just trying to help. Most bolt failures are not nearly this catastrophic- in my experience. But I have been wrong before
Lastly (or firstly) am glad you are OK. I have been there/ done that (somewhat).

Here is a similar "kaboom" from the past (ammo related) S&W AR kaboom
And another :Big AR KaBOOM
And again :KaBOOM
And lastly : Colt KaBoom

The list goes on and on- do a google search for AR15 Kaboom and most are ammo related, damage varies widely due to pressure differences.
Link Posted: 4/24/2013 8:05:23 PM EDT
ever hear  of Colt..............they make stuff even the  army uses
Link Posted: 4/24/2013 8:16:28 PM EDT
This bolt is an obviously badly heat treated POS.  It can happen to almost anyone, anytime.
Link Posted: 4/24/2013 8:28:49 PM EDT
[Last Edit: 4/24/2013 8:31:16 PM EDT by ricochet7]
Originally Posted By 4JSFORME:
I cannot recall where this particular bolt came form.   It was purchased probably 20 years ago when I was putting together this rifle.

Bolt / carrier fragments took out the entire upper receiver as well as other asundry parts.  The lower was unscathed (and more importantly, so was I)  The fractured bolt piece kept the rest of the bolt from turning and disengaging so the carrier stayed in place.  The primer in the case was gon ans well as hte portion of the pase of the case that was not supported by the fractured bolt.

I have easily put 1000 rounds through this gun without any issues. until now.  Was firing standard M193 ball, not reloaaded.

I have assumed that it was the bolt failure, and not ammunition related.  Any differing opinions?

Thanks for all of the help / comments (and sympathy).  I'll get it going again soon.

Joe


If the bolt is 20 years old and easily has 1000 rounds through it- I think the bolt would have failed sooner, similar to the recent bolt failures due to bad steel/bad heat treat.
And, when they failed, the damage was not this severe (and they usually failed in the first 30 or so rounds). Just again, my .02
Link Posted: 4/24/2013 9:15:53 PM EDT
[Last Edit: 4/24/2013 9:45:06 PM EDT by Mike_Anthony]
Originally Posted By 4JSFORME:
Had an "issue" with a bolt failure.  Can anyone offer me advice on this issue.  This was in a 10"(registered semi SBR) that has approximately 1000 rounds.  Portion of bolt fractured and destroyed carrier, upper receiver and mag.  Barrel is fine.  Was firing standard M193 Ball.

Any help would be appreciated

http://i1316.photobucket.com/albums/t616/4JSFORME/IMG_3838_zps2231a42b.jpg


This is most likely not a case of an improperly heat treated bolt, but more likely from a fatigued one. If it were, it would have failed much sooner than 1000rds. A 10.5" SBR requires more gas to cycle than a 16", so the gas ports are opened accordingly. Running a carbine length gas system on this type of setup produces a shorter dwell time, which results in higher chamber pressures present during the cycle. Also, the port tends to erode more quickly, allowing a higher volume of gas through the system with use. If you do not tune the cycle speed to permit the pressures to drop enough before extraction, this can lead to premature wear and stress on the bolt which can then cause catastrophic failures if a case rim is ripped to separation or even from a blown primer during extraction. This problem is exacerbated by using high pressure loads. If there was not a squib in the bore, then this scenario would be my next suspect during troubleshooting the failure.

ETA: can you post more photos of the carrier, case etc..?
Link Posted: 4/24/2013 9:17:40 PM EDT
Post a pic of the brass.



That really looks like a failure caused by severe case head expansion.
Link Posted: 4/25/2013 4:50:37 PM EDT
Obviously I still need to become more adept at adding pictures to these postings!



I fired several magazines of the same ammunition last week.  This time I loaded the mag and squeezed off four rounds and everything was fine.  Fifth round KABOOM.  Barrel is clear, gas tube was clear (and port).  The missing brass corresponds exactly to the portion of the bolt that broke away.  Barrel appears undamaged (inspected with a scope).  Portions of carrier ...missing...? (BFE?)  Remaining shells pounded out through magazine straight down to the concrete.  Bottom portion of magazine that extends out of lower is belled to approximately twice the original width.  Upper split down the middle and twisted.  Threaded portion of upper broken off completely.  Gas tube still engaged into key and carrier remained in forward position (or what was left of it) because the bolt did not rotate to disengage because of broken portion jamming/preventing rotation of bolt.



Thank you all for your comments / suggestions.

Joe
Link Posted: 4/25/2013 5:01:22 PM EDT
[Last Edit: 4/25/2013 5:06:16 PM EDT by ricochet7]
Jeez, am glad ONLY the rifle was damaged- that was a violent kaboom.
I've been shooting ARs since '70 or so, I've never witnessed a kaBoom like that one.
The bolts I've seen let go just sheared a lug or 2, others have broke in 2 at the cam pin.

Maybe it was just a bolt that was at the end of it's life. 50+K psi is a lot of energy.
I wish Pat Rogers still frequented here- he's seen almost everything with all the shooting he's been around.
Mike_Anthony may well be correct in his response. I still kinda think it was a bad round (when comparing to other kaboom pics).

Anyways, am glad you came out alright without injuries to yourself.

Edit--> I do believe the old mil-spec for bolts was 8620 and later changed to C158 due to longevity (does anyone know this as truth)?
The newer, shorter carbines (and SBRs) do beat the BCG more, shortening the life of the bolt.

Was the headspace ever checked when this SBR was built?
Link Posted: 4/25/2013 5:01:44 PM EDT
Here's an ArmaLite Tech Note that relates to your catastrophic failure.

http://www.armalite.com/images/Tech%20Notes/Tech%20Note%2049,%20How%20an%20AR%20Blows%20U­p,%2002.01.pdf
Link Posted: 4/25/2013 5:05:55 PM EDT
That is a classic kaboom, though yours had a bit more pressure than usual.



If you section the case it would look something like this:
















What you are seeing is a lot of brass that has entered into a fluid state, pressed back against the bolt face and spreading out from there (causing the split), forming a belt where the bolt meets the barrel face (where a slight gap exists), and generally flowing everywhere the pressure vessel allows it. First point of failure is typically a blowout at the extractor since that is the weakest area.




It takes a lot of pressure to make brass do that, much higher than you should expect a bolt to handle.




TL;DR - Your bolt didn't fail. The ammunition (or miniature nuke) caused this and whoever manufactured it owes you a rifle replacement.
Link Posted: 4/25/2013 5:13:55 PM EDT
[Last Edit: 4/25/2013 5:16:16 PM EDT by Mike_Anthony]
WOW!! That ranks up in the top 5 kabooms that I've seen. Looks like the chamber pressure was still way too high while extracting, rupturing at the rim where the extractor pulled. The brass is very soft during this time and being supported by the chamber walls at 30K to 40K psi on a carbine system with .223 and even higher on 5.56, but this looks like much higher pressure was present. Vented pressures couldn't quite stabilize yet and that is why the carrier also split in that manner. Most likely a very, very hot round, combined with a short dwell time.
Link Posted: 4/25/2013 5:23:01 PM EDT
No shit!  How did you not get all fucked up by it?  That's insane man I bet it sounded like the world had just ended..........
Link Posted: 4/25/2013 5:26:14 PM EDT
No way is that a bolt failiure.  That is overpressure ammo or barrel obstruction.  If it was a bolt failiure, you would have lost teeth on the bolt lock-up.  I would suggest you slug the barrel.  It may look fine, but still have a bulge due to squib. Wow
Link Posted: 4/25/2013 5:37:32 PM EDT



Originally Posted By Mike_Anthony:


WOW!! That ranks up in the top 5 kabooms that I've seen. Looks like the chamber pressure was still way too high while extracting, rupturing at the rim where the extractor pulled. The brass is very soft during this time and being supported by the chamber walls at 30K to 40K psi on a carbine system with .223 and even higher on 5.56, but this looks like much higher pressure was present. Vented pressures couldn't quite stabilize yet and that is why the carrier also split in that manner. Most likely a very, very hot round, combined with a short dwell time.


Generally you will see an attempt by the BC to retract and unlock the bolt (since the gas system is still intact) but it will get stuck due to the bent extractor inside the barrel extension.

 



The blowout has already occurred, long before gas system pressure reaches the BC's gas rings.
Link Posted: 4/25/2013 5:38:26 PM EDT
How about a pic of the case heads on the rounds that were in the mag.
Link Posted: 4/25/2013 5:53:16 PM EDT
Link Posted: 4/25/2013 6:18:22 PM EDT
Originally Posted By tumbleweed:

Originally Posted By Mike_Anthony:
WOW!! That ranks up in the top 5 kabooms that I've seen. Looks like the chamber pressure was still way too high while extracting, rupturing at the rim where the extractor pulled. The brass is very soft during this time and being supported by the chamber walls at 30K to 40K psi on a carbine system with .223 and even higher on 5.56, but this looks like much higher pressure was present. Vented pressures couldn't quite stabilize yet and that is why the carrier also split in that manner. Most likely a very, very hot round, combined with a short dwell time.

Generally you will see an attempt by the BC to retract and unlock the bolt (since the gas system is still intact) but it will get stuck due to the bent extractor inside the barrel extension.  

The blowout has already occurred, long before gas system pressure reaches the BC's gas rings.


That is usually the case, but with the carrier key sheared off and the vented side blown completely out, it looks like way more than enough gas may have circulated throughout the entire system. It is really difficult to determine the exact cause of these catastrophic failures though without being able to physically examine all the components. Thank God he was not injured. Until he posted those photos, I was under the assumption that this was a simple case of a bolt failure only.
Link Posted: 4/25/2013 6:59:47 PM EDT
It shouldn't be too difficult to figure out. Some things are known: brass becomes plastic at pressures way north of 100k psi and pressure peak occurs moments after the bullet has entered the rifling. If I recall correctly pressure curve peak (for a normal round) is at 1.5" of bullet travel. At 10" his residual pressure would be approx. 35% or 22k psi (again, with a normal round). Also, with a normal round, gas port pressure (carbine length) is in the neighborhood of 34k psi, yet you won't see anything near that level of pressure in the carrier key due to the restrictive nature of the gas system.






In this case where chamber pressure reached such high levels it is difficult to say how much of it reached the gas port and back into the carrier key. I'm guessing here but we no longer have a normal trailing curve but a huge step and falloff at case failure, when the pressure dump quickly drains the system of all residual pressure.







It's pretty safe to say most of the damage was caused by massive pressure released against the bolt, into the BC, down the magwell, and against anything in its way when the pressure vessel failed.

 
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