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Posted: 1/24/2010 3:32:30 PM EDT
I was sighting in a few of my most recent builds yesterday and had what I thought to be a failure to feed.  It just happened to be on my last round of that magazine so I cleared it and set it aside.  After further inspection, I noticed a couple lugs were missing.  I will be contacting the vendor tomorrow and will wait until then to disclose the vendors name and my customer service experience.  This occurred on the 18th round fired through this gun.  I shot 3 3 shot strings of AE223 55gr FMJ and then the bolt failed on the second to last round of a 10 shot group of Winchester Q3131A.

The barrel extension and chamber appear undamaged, but I'm not going to fire it until I talk to the vendor first.

Update:  I received the replacement bolt on Monday, only 1 week after calling it in.  The replacement does not have the TM stamp.  I hope to shoot on Saturday.










Link Posted: 1/24/2010 3:36:11 PM EDT
Never seen that happen on a brandnew bolt..those are usually the lugs to go though the 6th and 7th opposite right to left of the extractor..those are the un suported lugs.They look like they sheared identically with material from the bolt as well.
Link Posted: 1/24/2010 3:36:44 PM EDT
Vendor meaning a maker / vendor or just a middleman vendor?
Link Posted: 1/24/2010 3:39:16 PM EDT
I think that 95% of the AR parts "makers" out there are vendors as opposed to manufacturers.  This is a bolt from a site sponsor that sells parts kits.
Link Posted: 1/24/2010 3:41:20 PM EDT
It looks to me like the lugs on the bolt struck the lugs on the barrel extension––as if the bolt hadn't rotated properly.

Also, that BCG sure looks dry. I wonder what the manufacturer says about the situation.
Link Posted: 1/24/2010 3:41:37 PM EDT
Im sure the vendor will make it right but only he knows what machine shop it may have come from.Did it still run with the broken lugs?
Link Posted: 1/24/2010 3:42:41 PM EDT
Was the bolt fully tested, HPT and MPI?
Link Posted: 1/24/2010 3:43:38 PM EDT
Quoted:
Was the bolt fully tested, HPT and MPI?


this is what I would like to know as well.
Link Posted: 1/24/2010 3:43:43 PM EDT
Very interesting. I'm interested in who the vendor is and what they do for you.
Link Posted: 1/24/2010 3:43:51 PM EDT
Quoted:
It looks to me like the lugs on the bolt struck the lugs on the barrel extension––as if the bolt hadn't rotated properly.

Also, that BCG sure looks dry. I wonder what the manufacturer says about the situation.


The bolt carrier group was cleaned, then lubed with CLP in all the right spots with the excess lube wiped off with a paper towel prior to shooting.  Shooting temp was 5 degrees and lots of excess lube is not the best for shooting in that temp.
Link Posted: 1/24/2010 3:44:03 PM EDT
Don't really know what to say.  That bolt looks really dirty for the amount you shot. What's the spent cases look like?
Good for you to contact the vendor prior to bring out the torch.
Did you check head space on your build?
458
Link Posted: 1/24/2010 3:44:26 PM EDT



Quoted:


Was the bolt fully tested, HPT and MPI?


Oh boy, here it starts




 
Link Posted: 1/24/2010 3:45:05 PM EDT
was that from a del-ton?



Link Posted: 1/24/2010 3:45:20 PM EDT
Quoted:
Im sure the vendor will make it right but only he knows what machine shop it may have come from.Did it still run with the broken lugs?


It mechanically functions, but I did not fire it with the missing lugs.  After it failed I had a failure to feed with bolt parts in the area between the extension lugs and chamber and a few big chunks if bolt in the magazine.

Link Posted: 1/24/2010 3:45:55 PM EDT
Quoted:
Quoted:
Was the bolt fully tested, HPT and MPI?


this is what I would like to know as well.


I do not believe so, no markings to indicate this and the vendor does not advertise this.
Link Posted: 1/24/2010 3:47:15 PM EDT
Quoted:

Quoted:
Was the bolt fully tested, HPT and MPI?

Oh boy, here it starts
 


Not sure whey you would say that.

This is a failed bolt. Finding out if it was fully tested is the first question that poped into my mind as well.
Link Posted: 1/24/2010 3:47:40 PM EDT
Quoted:
Don't really know what to say.  That bolt looks really dirty for the amount you shot. What's the spent cases look like?
Good for you to contact the vendor prior to bring out the torch.
Did you check head space on your build?
458


The spent cases landed in the snow, but the few I picked up looked "normal"  I did not check the head space, the upper came fully assembled.
Link Posted: 1/24/2010 3:48:29 PM EDT
Quoted:

Quoted:
Was the bolt fully tested, HPT and MPI?

Oh boy, here it starts
 


Here what starts?  It's an extremely legitimate question.
Link Posted: 1/24/2010 3:48:37 PM EDT
Quoted:
I do not believe so, not markings to indicate this and the vendor does not advertise this.


Interesting; let us know what the solution is; I'm sure they will replace the bolt.
Link Posted: 1/24/2010 3:53:08 PM EDT



Quoted:



Quoted:




Quoted:

Was the bolt fully tested, HPT and MPI?


Oh boy, here it starts


 




Not sure whey you would say that.



This is a failed bolt. Finding out if it was fully tested is the first question that poped into my mind as well.


Yeah, I was kind kidding around with it cause everyone here seems to emphasize having a fully tested bolt. My bad.



Actually, I was wondering the same thing as you were. That is really supprising that the bolt failed so quickly. IMO there is no way that bolt was tested but I'm sure we will be enlightened soon.



 
Link Posted: 1/24/2010 4:26:31 PM EDT
Here's a pic of a marking on the bolt that I didn't notice before.

Link Posted: 1/24/2010 4:27:30 PM EDT
You were shooting in the snow? Holy cow, you can't do that with a new AR! (imagine Radar O'Reilly saying that) :)
Link Posted: 1/24/2010 4:34:53 PM EDT
I guess this chart say it all.

http://spreadsheets.google.com/pub?key=pwswheghNQsEuEhjFwPrgTA&gid=0
Link Posted: 1/24/2010 4:37:21 PM EDT
Link Posted: 1/24/2010 4:41:56 PM EDT
Tag for turn out. I don't recognize those bolt markings.
Link Posted: 1/24/2010 4:45:33 PM EDT


No, but you made it an email address...kind of.  
Link Posted: 1/24/2010 5:50:45 PM EDT
Is that a TM stamp? Thompson Machine???

How cold was it an how long where the rifles in this temp? Maybe the cold made the bolt brittle.
Link Posted: 1/24/2010 5:56:13 PM EDT
Quoted:
Is that a TM stamp? Thompson Machine???

How cold was it an how long where the rifles in this temp? Maybe the cold made the bolt brittle.


OP stated  "Shooting temp was 5 degrees"

Link Posted: 1/24/2010 6:05:42 PM EDT
Quoted:
Is that a TM stamp? Thompson Machine???

How cold was it an how long where the rifles in this temp? Maybe the cold made the bolt brittle.


It looks like a TM.  Rifle wasn't that cold, it was kept in the truck in a soft case for transport, then sat in the soft case for maybe 1 hour until shooting.  It was the 3rd rifle I was sighting in.  The metal didn't feel cold prior to shooting for what it's worth, but 5 degrees should be well within the operating temp anyway.
Link Posted: 1/24/2010 6:14:02 PM EDT
can I put my vote in for it being Colt....
Link Posted: 1/24/2010 6:21:55 PM EDT
Tag for outcome
Link Posted: 1/24/2010 6:29:09 PM EDT
Temp. would have no affect on a failure.  
458
Link Posted: 1/24/2010 6:42:58 PM EDT
it's a very clean shear, there's no peeling back of material - looks like poor heat treat making the metal too brittle which would account for it breaking so early on.  it broke at the weakest point but it's still a manufacturing defect.
Link Posted: 1/24/2010 6:55:59 PM EDT
Interesting...
Link Posted: 1/24/2010 7:01:16 PM EDT
I wonder if the bolt was mismachined.  It looks like the locking lugs broke cleanly off on either side of the extractor, maybe the extractor was pushing again them?
Link Posted: 1/24/2010 7:17:35 PM EDT
Quoted:
Quoted:
Quoted:
Was the bolt fully tested, HPT and MPI?

Oh boy, here it starts

Not sure whey you would say that.
This is a failed bolt. Finding out if it was fully tested is the first question that poped into my mind as well.

It's exceptionally doubtful that MPI would have detected the problem, that's why.
Quoted:
it's a very clean shear, there's no peeling back of material - looks like poor heat treat making the metal too brittle which would account for it breaking so early on.  it broke at the weakest point but it's still a manufacturing defect.

This is the reason why.  Almost certainly, the bolt didn't fail because it had two identical and symmetrical cracks from manufacturing... it likely failed because it wasn't heat treated properly and ended up too brittle.
Quoted:
I wonder if the bolt was mismachined.  It looks like the locking lugs broke cleanly off on either side of the extractor, maybe the extractor was pushing again them?

This is another possiblity, although with the rapid failure it seems less likely.  If this was the case it would be more likely that the locking lugs weren't engaging properly, either due to improper machining of the bolt or the barrel extension.
Link Posted: 1/24/2010 7:30:28 PM EDT
I'm guessing a cheap Bolt that was not MPI or HP tested.
Link Posted: 1/24/2010 7:54:19 PM EDT
Looks like a bad heat treat to me too. This is really the most common cause of gun part failure. I guess the good thing is that bad heat treat problems show up pretty early on so you can correct them. I had a friend a while back that had the mating surfaces of his bolt lugs mushroom over from a heat treating issue, kind of the opposite of what I think happened here.
Link Posted: 1/24/2010 8:27:13 PM EDT
You can do MPI and miss a piece of metal that will later break. MPI picks up existing cracks, not future ones.
MPI description

Have used this process for many years in the transportation industry to check for cracks. If you are well versed in this area you are familiar with MagnaFlux. MPI is a test, and like any test it can not find everything that can possibly go wrong. It is just a tool. There can be issues with the steel, being too brittle is one common problem, that can test fine at the factory but quickly fail in the field. It can happen to anyone's part, even your favorite "First Tier" parts. In the world of machines it just part of life.

Forget the name calling, blaming it on a lower tier maker, etc. Things do go wrong. I use to be a technical trainer with Toyota. They make Lexus, remember?. The highest quality cars made. Well, Toyota had a saying, "Nothing wrong is something wrong". Or, in simple English, there will always be problems. If you don't see them you are not looking close enough. Those people knew the truth, nothing is perfect.
Link Posted: 1/24/2010 8:43:47 PM EDT
Looks like a bad temper/heat treat and MPI would of found it. I say no on MPI.
Link Posted: 1/24/2010 8:50:19 PM EDT
Quoted:
You can do MPI and miss a piece of metal that will later break. MPI picks up existing cracks, not future ones.
MPI description

Have used this process for many years in the transportation industry to check for cracks. If you are well versed in this area you are familiar with MagnaFlux. MPI is a test, and like any test it can not find everything that can possibly go wrong. It is just a tool. There can be issues with the steel, being too brittle is one common problem, that can test fine at the factory but quickly fail in the field. It can happen to anyone's part, even your favorite "First Tier" parts. In the world of machines it just part of life.

Forget the name calling, blaming it on a lower tier maker, etc. Things do go wrong. I use to be a technical trainer with Toyota. They make Lexus, remember?. The highest quality cars made. Well, Toyota had a saying, "Nothing wrong is something wrong". Or, in simple English, there will always be problems. If you don't see them you are not looking close enough. Those people knew the truth, nothing is perfect.


this is correct
Link Posted: 1/24/2010 9:03:16 PM EDT




Quoted:



Quoted:

You can do MPI and miss a piece of metal that will later break. MPI picks up existing cracks, not future ones.

MPI description



Have used this process for many years in the transportation industry to check for cracks. If you are well versed in this area you are familiar with MagnaFlux. MPI is a test, and like any test it can not find everything that can possibly go wrong. It is just a tool. There can be issues with the steel, being too brittle is one common problem, that can test fine at the factory but quickly fail in the field. It can happen to anyone's part, even your favorite "First Tier" parts. In the world of machines it just part of life.



Forget the name calling, blaming it on a lower tier maker, etc. Things do go wrong. I use to be a technical trainer with Toyota. They make Lexus, remember?. The highest quality cars made. Well, Toyota had a saying, "Nothing wrong is something wrong". Or, in simple English, there will always be problems. If you don't see them you are not looking close enough. Those people knew the truth, nothing is perfect.




this is correct


Indeed. I completely concur. Also in the auto industry and I do a lot of quality testing. Weld breaking, sectioning and microphotgraphy inspection is my specialty.





I do want to note a couple things that haven't been covered:



First, the quality of the bolt assemby seems atrocious compared to all of the AR bolts I just took a peek at in my safe. The surface finish of the bolt body behind the lugs is horrible. Also, the diameter of the forward section of the bolt seems more than a tenth of a thousandth loose by the look of the carrier fit.  This is not the critical sealing dimension that is further back but it is an interesting observation.



Second is, that if the bolt body is that bad, one can only guess at what other steps were skipped in the assembly or Q.C. of that particular bolt.



A couple of good things that I noted. I do agree to the possiblity that MPI would not have caught this. To their credit: The vendor does not claim MPI or any other Q.C. process...so, at least they are honest about it.



Next, the OP has provided a good example of a failure we don't get to see a lot of. This makes for good discussion on several levels, not just Q.C.



Thanks to the OP for posting this.
Link Posted: 1/24/2010 9:05:36 PM EDT





Quoted:



Here's a pic of a marking on the bolt that I didn't notice before.





http://i56.photobucket.com/albums/g187/tysonwetzel/P1000872.jpg?t=1264382920



I have a bolt with that marking.  It was advertised by the vendor as CMT, but I recall seeing a picture on here of a DMPS bolt with that same marking.   The bolt carrier has similar rough machining.  Don't know what to tell ya.


 
Link Posted: 1/24/2010 9:52:14 PM EDT
Quoted:
Quoted:
Quoted:
Quoted:
Was the bolt fully tested, HPT and MPI?

Oh boy, here it starts

Not sure whey you would say that.
This is a failed bolt. Finding out if it was fully tested is the first question that poped into my mind as well.

It's exceptionally doubtful that MPI would have detected the problem, that's why.
Quoted:
it's a very clean shear, there's no peeling back of material - looks like poor heat treat making the metal too brittle which would account for it breaking so early on.  it broke at the weakest point but it's still a manufacturing defect.

This is the reason why.  Almost certainly, the bolt didn't fail because it had two identical and symmetrical cracks from manufacturing... it likely failed because it wasn't heat treated properly and ended up too brittle.
Quoted:
I wonder if the bolt was mismachined.  It looks like the locking lugs broke cleanly off on either side of the extractor, maybe the extractor was pushing again them?

This is another possiblity, although with the rapid failure it seems less likely.  If this was the case it would be more likely that the locking lugs weren't engaging properly, either due to improper machining of the bolt or the barrel extension.


Wouldnt the firing of a proof load have initiated/revealed the failure? MPI is only part of the proper bolt testing.
Link Posted: 1/24/2010 9:56:08 PM EDT
Here's a better pic of the broken off lugs.  The metal doesn't look the way I expected it too.

Link Posted: 1/24/2010 11:15:07 PM EDT
All of the M4 carbine bolt failure that US ARMY has experienced to date were made by a "top tier" manufacturer and HP tested, MPI tested.  
HP/MPI testing only means that if the part survives it isn't broke at the time of testing, not that cant or wont break in the future.
Link Posted: 1/24/2010 11:27:49 PM EDT
The only time I have seen a picture of a Bolt failure it's usually at the cam pin hole. I would replace it with a Bravo Company BCG or at the very least a Bravo Bolt and call it good.
Link Posted: 1/25/2010 12:40:23 AM EDT
Quoted:
All of the M4 carbine bolt failure that US ARMY has experienced to date were made by a "top tier" manufacturer and HP tested, MPI tested.  
HP/MPI testing only means that if the part survives it isn't broke at the time of testing, not that cant or wont break in the future.

Yeah but NONE of the US ARMY failures happened at 18 rounds.
Link Posted: 1/25/2010 3:01:56 AM EDT
Quoted:
You can do MPI and miss a piece of metal that will later break. MPI picks up existing cracks, not future ones.
MPI description

Have used this process for many years in the transportation industry to check for cracks. If you are well versed in this area you are familiar with MagnaFlux. MPI is a test, and like any test it can not find everything that can possibly go wrong. It is just a tool. There can be issues with the steel, being too brittle is one common problem, that can test fine at the factory but quickly fail in the field. It can happen to anyone's part, even your favorite "First Tier" parts. In the world of machines it just part of life.

Forget the name calling, blaming it on a lower tier maker, etc. Things do go wrong. I use to be a technical trainer with Toyota. They make Lexus, remember?. The highest quality cars made. Well, Toyota had a saying, "Nothing wrong is something wrong". Or, in simple English, there will always be problems. If you don't see them you are not looking close enough. Those people knew the truth, nothing is perfect.


100% correct, and well said. You can heat treat a bolt incorrectly and it will still pass MPI with flying colors. As far as shot peening, it would have done nothing to prevent this. No one to my knowledge Rockwell's every bolt they manufacture. No, not even Colt. At best they'll random a couple from each heat. The company I work for manufacturers Flight Safety Parts for helicopters. If a Flight Safety Part fails, it will almost certainly result in total loss of vehicle, payload, and crew. There is no higher degree of traceability in the manufacturing process that exists. Helos still crash. Just because a part is exposed to this type of testing does not mean a failure can't or won't take place. One has to look no further than the fan disk that disintegrated in the Sioux City DC-10 crash. 111 people died. That part passed any and all inspections and tests at the time of manufacture. Yes, it is obviously better to use these type of tests, but it is nowhere near a guarantee that a failure will not occur.

Link Posted: 1/25/2010 4:00:33 AM EDT
Quoted:
Quoted:
You can do MPI and miss a piece of metal that will later break. MPI picks up existing cracks, not future ones.
MPI description

Have used this process for many years in the transportation industry to check for cracks. If you are well versed in this area you are familiar with MagnaFlux. MPI is a test, and like any test it can not find everything that can possibly go wrong. It is just a tool. There can be issues with the steel, being too brittle is one common problem, that can test fine at the factory but quickly fail in the field. It can happen to anyone's part, even your favorite "First Tier" parts. In the world of machines it just part of life.

Forget the name calling, blaming it on a lower tier maker, etc. Things do go wrong. I use to be a technical trainer with Toyota. They make Lexus, remember?. The highest quality cars made. Well, Toyota had a saying, "Nothing wrong is something wrong". Or, in simple English, there will always be problems. If you don't see them you are not looking close enough. Those people knew the truth, nothing is perfect.


this is correct


Yes... things do go wrong.  But given that the bolt failed so early, this was a serious flaw in the material or processing (looks like a bad heat-treat to me), and I think a HP test followed by an MPI would have probably found the problem.
Link Posted: 1/25/2010 4:03:17 AM EDT
Quoted:
All of the M4 carbine bolt failure that US ARMY has experienced to date were made by a "top tier" manufacturer and HP tested, MPI tested.  
HP/MPI testing only means that if the part survives it isn't broke at the time of testing, not that cant or wont break in the future.


But how many of them occur withing the first 18 rounds?  USGI bolts are usually good for 9-10,000 rounds.

The HP test before the inspection is intended to ferret these early failures out.
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