Bravo Sir.  I completely agree.  Bushy (at least before they were bought out by Freedom Group) batch tested bolts.

It depends....individual testing vs batch testing, etc, will alter price.

Was it HPT'd as well?  I believe MPI is pointless unless it is HPT'd first.

What ammo were you using?

That's great.  The rest of the serious use AR world does.  I could care less what boutique brands do / think.

While I would not call it worthless.  It definitely means a LOT less without prior HPT.  

 

Everybody gets their panties in a wad when this comes up - it is a $40-50 part to replace that will eventually break regardless of who manufactured it or what inspections they did.

Paying an additional $200 on a rifle to hedge my bets that a $50 part won't break is a poor investment IMO. Buy spares and keep shooting - I keep one in my pistol grip since it has critical parts like the ejector, extractor, gas rings, and respective springs which are all prone to breakage or wear out.

If MPI makes you happy and you honestly believe that there is certified technician scrutinizing every bolt for 5 hours to detect any micro-flaws, then get MPI.  You can get welding dye crack penetrant and inspect your whole collection whenever you want for $21 at Grainger (Spotcheck Dye penetrant).  This is still cheaper than buying several of the companies that use things like "spec" "SOCOM" "Tactical" and MPI as marketing tools.

This was likely a result of a poor heat treatment and would not show up under MPI inspection (which it obviously didn't).  The company will likely send a replacement, but your backup will keep you shooting while you wait for warranty to come through!

Larue...botique...sure if you say so.  KAC...no not in the slightest....

Centurion does not HPT their bolts either. Hardly a boutique brand.

I heard this as well.  That something like 1 bolt in every million got rejected and that it was totally pointless.

So your bolt breaks and, suddenly, inspections are a worhtless marketing tool?  Too small of a sample, bro.

MPI by itself is worthless without HPT.

I would really like to know what percentage of bolts are failing HPT/MPI testing.        
 

I think the premise of your initial post was that just because a bolt is marked "MPI," that does not make it infallible.  I would agree with that.

I was reading your post to say that "my bolt was MPI'd, and broke, therefore MPI is worthless."  

It think the lesson here is that all parts can break, and having a spare bolt handy is always a good practice.

Admittedly, I'm far from an expert as it relates to metallurgy and testing procedures, but could this likely be an issue of improper heat treatment?  Would HPT and MPI be likely to catch an issue with improper heat treatment?

PSA sells BCGs with MPI bolts for $70, I'm unconvinced it adds significant cost to the end product.

Nobody has said it yet, but Magnetic Particle Inspection (MPI) is what is referred to as a Non-Destructive Test (NDT). In layman' terms its purpose is to find cracks on the metal's surface and just a tad deeper.

I have a couple beater rifles with quality non-MPI'ed bolts that each have thousands of rounds though them.  I have nicer high end rifles (factory and builds) with MPI'ed bolts with thousands of rounds through them also.  Never had an issue with either in the past.  No way of really knowing what the figure is, but the fail rate for either is likely very low for a newer (as in not used to the edge of its service life) bolt.

FWIW KAC doesn't MPI or HPT. But they also have a different, upgraded bolt design.

All things being equal on a stock bolt I prefer it as it seems to go hand in hand with quality, but at same time shit does happen. Colt had a run of bolts a while back that broke at the cam pin hole at under 100 rounds.

cms81586,

What are the specs of the weapon that the bolt failed in (gas system, barrel length, gas port diameter, action spring and buffer weight, carrier profile, and extractor spring setup)?

MPI only detects occlusions on or near the surface. If the bolt is machined from a billet there is always a chance of an internal defect that happens to be in an area of high stress/small cross-section and thus can lead to failure.
I care more about HPT and shot-peening as these verify the strength of the bolt to withstand an over-pressure round and relieve stresses from the manufacturing process to increase the fatigue life of the bolt, resp.





Edit: That's an odd place for a bolt to fracture. The only operation that places stress on the tail of the bolt (behind the cam pin) is when you manually rack the charging handle. When a round is fired, there's a bearing stress on the bolt from the cam pin, but that should not cause a fracture like yours. You should check the cam pin and the cam groove in the carrier for grinding or something else that would put the bolt under torsion.



N/M it happens. Probably a bad heat treatment.



 

Marketing likely has something to do with it, but it can't be the only reason.

If the point of your post is that MPI does not provide a guarantee, then I wholeheartedly agree with you.  But frankly, I've never seen anyone claim that it is a guarantee.

It may very well be the case that HPT and MPI are becoming less critical these days, but if it were completely unnecessary, it does not seem rational that the majority of the most well respected mfg's are still doing it.

No disrespect to you (and I sincerely mean that), but if Paul Buffoni comes out and says that they find it to be unnecessary, I'm willing to give more credence to his views than yours.

If BCM stopped doing it tomorrow, I likely would not hesitate to continue to purchase their bolts.  They are the pros and they have built a stellar reputation, so I'm more likely to accept it if they are finding that it is unnecessary.

I believe that KAC forgoes HPT on their bolts.  I'd rely on their bolts even without HPT because of their solid reputation for R&D and testing.  KAC Id' trust......some others not so much.

And they still manage to last 4-5x longer....although some of that can be attributed to the design changes...

No disrespect taken...and don't think that I'm trying to claim a non-MPI Model 1 Sales / M&A Parts bolt is the same as an MPI'ed bolt from a quality MFG.  And believe me...there are plenty of people out there that wouldn't clear their moms basement with a rifle unless it had an MPI'ed bolt...