Does anyone have reliable knowledge of  bolts not MP inspected (or adverised that way) failing signifigantly more than say.. colt, cmt  ,don't about BM orDPMS ,LMT  ...           thanks from a new poster ar-15.com

Welcome aboard!

But you will have to give us more information on what exactly you want to find out about bolts? What type of "failures" are you refering to? etc.

There are a lot of bolts here that are made in the Philippines, and if i recall correctly, do not have the MP stamp. But they are reliable and have gone thru a lot of shtz in combat in the jungles of Mindanao.

DPMS bolts are known for their high failure rate, esp. when used with 5.56 ammo.

Their tolerances on the lugs are poor, and often times 1 is longer than the others and takes all the stress, then eventually sheers.

though i have not experienced any types of failures with any of my bolts nor do i want to, the dpms bolt i have does look to be the first one to do so.



really bad machining and what not compared to the others i have.

I do not have any first-hand experience with bolt failure (I only use Colt bolts) but I have seen many pics and threads about Model 1 bolt lugs sheering off.

Become a Team member and do an archive search!  

Most bolt failures are the two undercut lugs on either side of the extractor.  The ACB addresses this not undercutting the lugs.  It is also reasonable to surmise that these 2 lugs take an added load, even if slight.  The extractor lug is not structural to the bolt and forces would be applied non-uniform fashion.

This is a 499 ACB but you get the idea.  Note there is no undercut for the extractor.  


As for MP vs Non MP, this type of failure shows up in both.  I would imagine a bolt that showed no flaws after a 70,000 PSI proof round had a better chance at a long life than an unproofed bolt or they would not require it.  The mil replacement schedule for bolts is less than 10K rounds, allthough I doubt if they actually adhere to that.  I have no idea how many bolts fail MP testing.  That would be some interesting info!  If the number is significant, I would say MP testing would have a sig effect on preventing these types of failures.

48thHighlander, thanks for sharing.

For me, "MP" makes me a little more secure.

As well it should!  Luckily, most bolt failures do not result in a KABOOM which is a great thing about the AR.  Say a FAL has marginal headspace and it stretches.  NOT FUN.  Do not ask me how I know.

I was a weapons tech in the Canadian Forces and I never saw a C7 bolt fail.  We did not track rounds fired either to replace the bolts.  

I had a bolt failure in my Bushmaster about 4 years ago.  All of the lugs were ripped off with no kaboom.  All that I noticed when the shot went off was a slap from the trigger.

hadn't had any to fail yet, But Welcome to the site

Does anyone know the main causes of bolt failures and whether or not MP testing is capable of catching those defects?  I'm thinking improper alloy or heat treatment as a possible cause.  Would MP testing indicate there was a problem there or not?  I thought all it did was assess internal grain structure, i.r., make sure there's no hidden, burried cracks.  Does it do more than that?

rdthreading,

In my experience the majority of bolt failures I have witnessed or where I repaired the weapon afterwards were from commercial bolts. This also includes BM and DPMS. Not that I'm trying to condemn their products offhand, as everyone puts out a bad part now and then.

It must be remembered that any commercial company has to make a profit at the end of the day to survive. So, if they can produce a safe and functional bolt without the added expense of M (magnetic particle) and P (high pressure proof load) testing it, they will to keep their prices competitive. If not, they would surely have to pass the added expense on to you, the consumer. And lets face it, they know that 99% of those consumers probably are unaware of  MP testing or just don't care as long as their rifle is functional and they got it at a good price. Plus, 99% of those rifles will in all probability only be fired for recreational purposes where a failure rate of even 5% would only be an inconvenience to both the manufacturer and the consumer as bolt failures in themselves seldom result in a catastrophic failure resulting in injury.

That is not to say I've never seen a military MP tested bolt fail, I have. But the majority of those failures did not originate with a faulty bolt. They were the result of bore obstructions(squib rounds, cleaning rod sections, patches or muzzles plugged with dirt, etc) or reassembled and fired without the cam pin which resulted in catastrophic events. These bolts usually suffered one or more sheared lugs, brake at the cam pin hole or both. I'd hate to see the results of the same with bolts that were not MP tested. Conversely, I have seen a high percentage (in comparison) of commercial bolts that suffered those same failures as the result of normal use and NOT a catastrophic event. Though as I mentioned earlier these failures seldom result in injury.

So, do MP tested parts cost more, sure they do. But MP testing in itself is not the only guarantee of quality. Has the bolt been properly deburred or does it have sharp edges. Are the leading edges on the rear of the bolt lugs beveled where they will make a smoother transition into the barrel extension or not. These two manufacturing steps are also indications of quality as they help reduce the stress on the bolt thus prevent failures. Companies that care enough to spend the extra money for MP testing usually do so after they have fully machined, stress relieved and properly heat treated those parts without cutting any corners. As to do otherwise wouldn't make financial sense.

Bottom line is that if you buy from any of the big brand names you will be all right even if they don't MP test their bolts, or barrels for that matter. If you should have a failure they will stand behind their product. Now if you want the added assurance that buying a MP tested bolt brings, or will be using your weapon for other than recreational purposes then it makes sense to buy Colt, LMT or the new offerings from CMT. Surplus military Colt and FN are also good deals when you can find them.

All that being said, you must ask yourself what you intend to use your rifle for and buy accordingly.

Wpns Man  

Quoted: MP sees only external cracks.

I am not sure what type of MP test they are using, but in general MP testing can detect surface and sub-surface defects depending on type of test.  For example a AC (alternating current) test detects surface defects only, and DC (direct current--either half-wave or full-wave) test detects surface and some sub-surface defect.  They say some as a lot of factors go into "depth of penetration" of the DC field.

Quoted: Quoted: MP sees only external cracks. I am not sure what type of MP test they are using, but in general MP testing can detect surface and sub-surface defects depending on type of test.  For example a AC (alternating current) test detects surface defects only, and DC (direct current--either half-wave or full-wave) test detects surface and some sub-surface defect.  They say some as a lot of factors go into "depth of penetration" of the DC field.

+1

Magnetic particle inspection is a nondestructive inspection method used for detection of surface and subsurface flaws in ferrous materials.  It can be used to inspect many different parts such as forgings, weldments, castings, etc.  The inspector can choose a dry or wet inspection method and/or visual or fluorescent particles for daylight or UV inspection.

Quoted: Good post WM! C4

+1

And that's why all my ARs have Colt bolts and carriers.

thanks to all for info photos & links  ,very good web site

Originally from C4i Grant

I took Pat Roger AAR class in August. He showed me the running catalog of broken gear. A majority of the items that were broken were Bolts (with sheared lugs). A good portion of those bolts were BM.

One of those would be mine......

I lost the lug on the bottom side of he extractor. but in fairness. That bolt was made in 94  and had over 10K rd count. and it kept working all day. I only realized the failure at the end of the second day of clas when I ws cleaning it....
And Bushy replaced it with a complete new Bolt for free.....

No free lunch and no guarantee's in life. I'll let ya know when this new bolt fails......
But based on statistical data, the Colt Bolts are gonna be less prone over a large number vs the 2nd tier makers.
I sleep fine at night with my bushmaster in the corner.

Snap-on tools break, so do Craftsman,Matco, etc, etc. their all tools. most shooters will never shoot their AR's in a lifetime to find out if their bolt will fail or not, don't loose any sleep over it.... just go out and shoot....

Lost a lug after 12K+ on a M1S bolt.  Lost a second lug 600 rounds later.

Quoted: Lost a lug after 12K+ on a M1S bolt.  Lost a second lug 600 rounds later.

wow, 12k.  maybe one day Ill get to shoot mine that much.

MP bolts for me, whether Colt or CMT.

Quoted: Lost a lug after 12K+ on a M1S bolt.  Lost a second lug 600 rounds later.

Lost a lug and kept shooting?  Hardcore!

I didn't have an extra bolt (yeah, shame on me).  'course, after the second lug, I figured I just passed my safety threshold.

Quoted: Does anyone know the main causes of bolt failures and whether or not MP testing is capable of catching those defects?  I'm thinking improper alloy or heat treatment as a possible cause.  Would MP testing indicate there was a problem there or not?  I thought all it did was assess internal grain structure, i.r., make sure there's no hidden, burried cracks.  Does it do more than that?

This thread on bolt failures has a link to an interesting article: www.ar15.com/forums/topic.html?b=3&f=118&t=247898

Note: Complete article is included later in thread.

Quoted: Quoted: Quoted: MP sees only external cracks. I am not sure what type of MP test they are using, but in general MP testing can detect surface and sub-surface defects depending on type of test.  For example a AC (alternating current) test detects surface defects only, and DC (direct current--either half-wave or full-wave) test detects surface and some sub-surface defect.  They say some as a lot of factors go into "depth of penetration" of the DC field. +1 Magnetic particle inspection is a nondestructive inspection method used for detection of surface and subsurface flaws in ferrous materials.  It can be used to inspect many different parts such as forgings, weldments, castings, etc.  The inspector can choose a dry or wet inspection method and/or visual or fluorescent particles for daylight or UV inspection.

UT is generally the standard for subsurface NDE inspection.  I would imagine most of the mag particle inspections being performed on these bolts will only show surface indications.

DHH,

Thanks for posting the link. I missed that discussion but I've been kinda busy for the last few months. It was a good read and I'm glad they discussed the importance of proper stress relieving and heat treating. Those two items are often overlooked when the topic of bolt quality is discussed, and was one of the points I was trying to get across.

wyv3rn,

Any chance the manufacturer of the failed bolts was mentioned in the report? Based on my experience, I have a pretty good idea of who it might be as they had some QC problems in the early 90's though they have long since squared them away.

Wpns Man

Quoted: Any chance the manufacturer of the failed bolts was mentioned in the report? Based on my experience, I have a pretty good idea of who it might be as they had some QC problems in the early 90's though they have long since squared them away.

Take a look at the close ups of the bolts, they have the older style bevel cuts on the bolt lugs.  I figure they date from 65-82, so they could be Colt's, H&R, or Hydramatic.

The rifles are described as being M16A2's, so best guess is that these are old M16A1 rifles rebuilt as M16A2's.  As you know the "conversion kits" do not include a new bolt group.

Ekie,

Rebuilt rifles with high round counts are a distinct possibility if these came from a training post. The bolt pictured does have the earlier stlye bevel cuts. It appears that figure 5a - 6 are of the same bolt. It would have been nice to have pictures from more of the failed bolts, to include the manufacturer's markings to draw a more accurate conclusions from. The pictures do show a classic example of bolt lug failures I have witnessed regardless of manufacturer or time period.

wyv3rn also mentions some QC problems in a later post in that thread. That would help confirm a experience I had with this very issue was probably not an isolated case. As I think it is around the same time frame. While the numbers of failures were not great, they were noticable and all from a certain manufacturer.

Wpns Man

Yep, would have been nice if that report contained more info, and pictures.  Odds are the bolts in question are Colt's, in that the vast majority of USGI bolts in that configuration were made by them.  

I received a Deltaforce catalog (www.deltaforce.com) and they had titanium bolts. What is everyone's experience or opinion on those?

Those bolts are titanium COATED, not pure titanium.

Quoted: I received a Deltaforce catalog (www.deltaforce.com) and they had titanium bolts. What is everyone's experience or opinion on those?

Titanium coated parts have reliability issues...

Stick with original OEM parts for the most reliability...

Sorry, I failed to mention it was a coating. Thanks for the feedback.

Hopefully my RRA Entry Tacticle will hold up for awhile. It is brand new. I do like an earlier suggestion of buying a replacement bolt and keeping it stashed in the verticle handle. I may do just that.