Not if the condition, (i.e. crack), didn't occur during the heat treat process. As was mentioned, MPI will only find existing cracks, not future ones. If the bolt was heat treated too high, (Rockwell), it could have fractured on the first shot. In this case MPI would have been useless simply because the bolt would have passed.  

Did you miss the part about the HP test?  The HP test is done at much higher chamber pressures than normal, and is specifically intended to weed out such "infant mortality" failures.  Some argue that the test reduced bolt life (and they may be right), but I'll trade bolt life for increased reliability early in life any day of the week.  This is why MPI on it's own is MUCH less useful than MPI in conjunction with the HP test.

It is possible, of course, that the bolt could have still passed an MPI after the HP test, but I think it's far less likely.  

I think the OP got bit by an untested, poorly heat-treated bolt.

I agree, (at least about the poorly heat treated part.) That type of fracture is usually the result of too high of a hardness. Heat treating is not always an exact science simply because of the difficulty in duplicating exact composition from heat to heat. This is why in the aerospace industry much of the steels used need to receive several draws, with certification to accompany the procedure used. This is simply far too expensive for gun makers to undertake. Failure because of bad processing is also difficult to predict. Several metallurgists concurred after examining the ruptured fan disk from United Flight 232 that it should have failed the first time the engine was spooled up to takeoff power. It did not.

BCM has this done as well.  I was under the impression that LMT did this also.

QFT

thanks for sharing this, i learned something today

For this discussion to be truly meaningful it needs real world verifiable  statistical data that shows what percentage of parts break after a) being proof  tested b) not being proof tested. Then one would  need to failure rates in the field, average life span, all sorts of data. Looking at one bolt failure and then trying to draw any sort of meaningful conclusions from it is a joke. Just like those who claim everything except this month's favorite rifle is a joke.

It is a good thing to analyze failures and learn from them. But you can not look at one case and learn much other than that one part was bad. Its also like basing opinions on hearsay, rumors, junk you read on the internet, my ex-brother-in-laws buddy,  etc. Some will use this one case to call this or that companies stuff as "junk". Outside this microcosm of of a website there are many thousands of folks who never heard of this and are having great service from their "low tiered" "junk" rifles.

This bolt broke. Its a an isolated case, hopefully!.  Who knows. Maybe this bolt  had a weak spot and then was subjected to a massively overloaded round in the rifle and it let go. You don't have all the facts to know. Anyone who claims to know exactly what caused this is blowing smoke. Sure, we can, and should always, question, speculate and try to find out. But folks, there is just so much you don't know and sitting at your computer and telling the world that only Colt and FN are good and the rest is junk doesn't fly in the face of any experienced, knowledgeable, thinking people.

Yes, it would be nice if everyone did those tests. Yes, doing them is better than not doing them. But, let's see some real factual statistical data that supports what you are spouting out. Otherwise, its just advertising for your personal favorite brand. My RRA, Armalite, JT and others have never failed me. But if I believed everything I read on this site, I would junk everyone of them.

Same ole "but my XXXX has been flawless."  Yes.  I sure they have.  If 10% of those rifles (an exaggeration I'm sure) fail early in their life, that would still leave 90% not failing.  Those 90% are happy, but what about those 10%.  If they're just shooting at the range, no big deal.  But if they're shooting MFers in A-stan, or trying to deal with a home intruder, then 10% seems like an unacceptable level of risk.  Just saying.... how much is your life worth?  Mine is worth paying for better quality, tested parts. I don't want to spend "go time" worrying about if I won the bargain-bin rifle lottery or not.

FWIW, I'm sure that those companies who produce tested bolts keep track of the stats.  And I'm sure .mil does as well as they can tracking failures.  But I would doubt that a company would let such proprietary information out to no advantage.

The truth if it ever were spoken !!

Proof testing is done on a great many makes of firearms besides Colt and FN. It's one of the reasons Ruger revolvers are so filthy when you open the box. They do not clean them after proof testing. All 5 of my Bushmasters had brass marks on the case deflector from being factory tested before shipping. This isn't something new.  

Test firing and proof firing are not the same thing.

test firing the rifle 10 shots isn't the same thing as HP testing and MPI-ing the bolt.

If it came from a "parts kit" vendor then no, it was not.




ETA - And holy fucking shit that barrel has a ridiculously out of spec gas port. 18 rounds and the bolt face has that much brass on it?






 

BCM Bolt Specs:

Milspec Carpenter No. 158® steel
HPT Bolt (High Pressure Tested)
MPI Bolt (Magnetic Particle Inspected)
Shot Peened Bolt
Chrome Lined Carrier (AUTO)
Chrome Lined Gas Key
Gas Key Hardened to USGI Specifications
Grade 8 Hardened Fasteners
Key Staked Per Mil-Spec
Tool Steel Extractor
BCM Extractor Spring
Black Extractor Insert
Mil-Spec Crane O-Ring

I can count the number of companies I will do business with on one hand.  BCM is one of them.  I do trust that the specs they claim on their products are accurate.  I am aware they are not manufactured in house.

How do you know they're NOT proofed? It is to their advantage to do it, and it costs them no more. Many manufacturers have proof marks stamped right on the barrel.

Thanks for this post.  One bolt does not make a set of data.  The purpose of this thread is to show people that parts break and spares are a good idea.  I spoke with Del-Ton this AM and they are sending me a replacement bolt today.  They did request that I send them the broken bolt, but they did not ask that I send the upper back.  I would rate the customer service experience with Del-Ton as very good so far, no hassles about what ammo I was shooting or my purchase date or anything like that.

I would also like to point out that, to my knowledge, Del-Ton did not make this bolt and I do not hold them accountable for any QC or manufacturing errors that may have occurred.  Parts break and things happen, what's more important to me is than when things happen, how are they dealt with.

Huh?

"Hobby guns" are typically overgassed. That is no exception.



 

So how does that connect to more brass on the bolt face?  Not being obtuse, just want to learn.

ETA, I will check the other Del-Ton, MA and Stag that I shot that day as I haven't cleaned them yet.  Would the 5 degree shooting temp have anything to do with it?  I'll make sure to gauge the gas port when I'm in there next too.

http://www.ar15.com/forums/topic.html?b=3&f=118&t=413742&page=1
http://www.ar15.com/forums/topic.html?b=3&f=118&t=425345&page=1
Well, the MPI stamp on a bolt is mostly worthless anyway.  To quote Keith_J from one of the linked threads, MPI is a "cargo cult".  What you need for a quality bolt is to use a quality material and have tight control over the heat treatment process, and most likely run other quality control tests to ensure the heat treatment is correct, which MPI cannot do.  Materials and material science have advanced considerably since the HPT/MPI testing was devised and that testing is really an anachronism.


Actually it is for the most part, at least according to people who know.

MPI only detects surface cracks. Any bolt that had a surface crack that would be detected by MPI will almost certainly fail completely within a handfull of additional rounds shot.

IMO a FAR more useful testing proceedure would be to destructively test a sample bolt from each heat treatment batch (and even material lot) to ensure proper heat treatment qualities.  That plus say a 10 round test fire would be a more effective QC than the current military specified test.

DPMS?

As demonstrated here, the test fire process obviously needs to be 18 rounds.

Testing the heat treat batch would have revealed the over-hardening and should have binned that batch.  That bolt should not have made it to test fire.

An alternative explanation is a machining dimensional problem with either the bolt, barrel extension, or even the bolt carrier, which concentrated forces on those two lugs.

Any indication where DEl-Ton got the bolt?

Just the stamping that I photoed on page 1.  TM, somebody said it was Thompson Machine, but I'm not sure.

I had a batch of these bolts in my Tok/7.62x25 builds. They lasted around 100rnds & failed. They were over heat treated. Delton replaced them without issu. I figured if these bolts made it into a 5.56 they would not last long!

<sigh>  no... you missed the point.  HP testing is done at much higher pressure than normal.  It will bring out flaws in materials that might not surface for hundreds of rounds otherwise.  Firing 10 rounds is not going to do anything but ensure the rifle was assembled reasonably correctly.  

Tyrex13



Yuppers.. just as I figured, Cheap ass bolt built to absolutely no standard... And if Del-Ton sells it, it's there's as they CHOSE to use this vendor...

Valuable lesson this thread is... Buy cheap shit.. have broken shit....

If any of you remember over five years ago I was trying to find the answers to questions about just who Mfg's the bolts for many of the AR makers. and I really got no really good answers. I wanted to know how a AR maker would really know if a failed bolt was theirs. One AR makers Engineers told me they knew their machine work. I asked their bolts were not marked with their name or Logo. Answer our customers don't wish them marked.
I just picked the ARs bolt for my search, because it was IMHO the weak link of the AR.

A lot of forum members gave me the letters and numbers that they felt gave some hint of the bolts Mfg. and test history. That's about all I ever really found out, and it was not much.

Thompson Machine was just a guess. I don't even know if they make AR parts besides naked lowers and building .22 setups. They are a homegrown back woods shop that makes suppressors and things.  They look like they have good machining.

That bolt marking kinda looks like an  I M also. Isrealie Military Industries?

I know the operating temps where fine for for a regular AR but 5degrees probably didn't help for an overly hardened and brittle bolt.

While MP testing may not have detected this failure, a company that would avoid HP/MP testing might also avoid basic stuff like proper heat treatment...

The bolt is one of the most critical parts on the rifle...don't go cheap on it.

Thats why I only use Les baer wich is made by Youngs MFG for chromed Bolts,Colt,BCM,for regular parkerized Bolts..More BCM bolts than anything else though.

I pulled the bolt out of my del-ton upper to check the marking and mine has the letters WTC and is read upside down of that one.

It is assuredly Del-Ton's responsibility if it passes through their hands. So lets hear from others with experience from Del-Ton. How has their equipment, bolts in particular, held up?

Good evening all.

What a learning experience this past year has been.

I've learned from the great knowledge base that is arf.com how to build two wonderful Frankenplinkers. I now have two of the finest designed battle weapons ever devised by man. Two rifles that I never would have been ever able to afford as brand name rifles are either ridiculously over-priced or completely unavailable here in the great middle of nowhere Maine.

My first build runs a Rock River Arms bolt carrier group and my second build runs a Del-Ton bolt carrier group.

~500 rounds through the first build w/RRA bcg without any failures of any kind, even when using dozens of reload recipes.
~100 rounds through the second build w Del-Ton bcg with the only failures caused by unusually long Hornady 68 HPBT Match bullets.

The RRA bolt has the letters "CM" stamped into it.

The Del-Ton bolt has the letters "WIA" lasered into it.

I doubt either bolt will ever fail me because I don't abuse things I want to keep around.

There are up-sides and down-sides to the vastness of knowledge on arf.com.

Up-sides being my case of poor slobs who work their asses off all week and want something enjoyable to tinker with and plink with on the weekends and building  great rifles with the know-how on this site. How to fix something that might break. How to improve something. Wonderful place.

Down-sides being the palpable, sometimes weird, arrogance of some members. "I bought/built a rifle that costs five times what a 'bottom feeder' rifle costs. I'll be able to kill five times more zombies than you. And if you don't buy/build a rifle like mine then you're the biggest piece of *%&# looser on the planet"

And the vastness of knowledge also means that RRA or Del-Ton have literally 100s of thousands of bolts pass through their hands and into the end-user's hands; if two bolts fail they'll sure as *#$! find their way here.

Without hard numbered failure rates solidly attributed to known manufacturers then it's completely useless and arrogant to call some-one's bolt a piece of #@!* just because of the retailer who sold it or the price paid for it.

tyrex13, I'm glad to here that no-one was injured in the failure (did any zombies get away?) and that Del-Ton's customer service is gtg.

Where were you shooting at???

Birchwood from about 2-4pm.

How does overgassing contribute to brass on the bolt face?

I have a similar bolt issue. My bolt has the same TM marking on it and broke on me yesterday. I have 160 rounds through the gun and it happened on number 161. On mine only the lower side broke off and I thought I had a jam, but the broken piece was in the way of the bolt. I have been reading on this site for some time and decided to join when I saw this post. I bought my upper assembled from a local guy who sells them at the local and Portland, OR. gun shows. He's a good guy and I know he'll stand behind it. I am more interested in where all of the parts for my upper came from now. It was good to find this post and see that this isn't an isolated incident. I love this site, thanks for all the info!

The bolts on H&K 416's are having the same problem. There is a replacement for them currently being offered.

It is my understanding that the lugs on either side of the extractor cut out take a disproportionate amount of the initial pressure on the bolt.  They are the most likely to break.

IMHO there is a difference between gear (not just ARs) that is REALLY designed and built for critical use where a life may be on the line and sporting gear where a range session or a match might be compromised.  The thing is to learn the difference and make your choices: quality-reliability vs $.

It is interesting that the three M1 carbines I own all have the marks of a Rockwell hardness test on every critical part (a small dimple) and these were manufactured in the middle of WWII.  I have come to believe at least SOME of today's manufacturers don't really know/care the importance of certain QC procedures - they are "business men"* - not engineers and if it passes muster with their product liability lawyers, it is cheaper to let the end user do the final endurance/QC testing.  Good customer service is apparently cheaper than good QC

The old saying: "there is never time to do it right but there is always time to do it twice", comes to mind.

* In the derogatory sense of the word: profit before all else,

jb weld it.

jk

During a pre mission test fire, I had my bolt on my Colt M4A1 break when firing M855 ammo.  This is with a MPI/HP tested bolt.  Carbine had many rounds through it and was on my second deployment with same rifle.  Luckly, I had a spare M16A2 that I borrowed its bolt for the mission.  Got it fixed after the mission.  Remember that they are all mechanical devices that can fail.

CD