A $400 complete upper should sound the alarms.
Unless it cracks through to the surface during the HPT, the MPT can’t do anything.
Being a little known company, I doubt they had their MPI techs trained to the mil std and who knows what type of materials/equipment they used to test it.
I don’t know if I’m ‘enlightened’ or not, but I’ve maintained my MPI certs for 14 years. I’ve MPI’d lots of stuff. Little stuff like nuclear reactor parts, turbine parts, off-shore oil well parts, shit like that.
I stand by my statement when I say it don’t mean shit.
Why am I not surprised?
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You perform MPI yourself on a professional level, and yet you frame your peers at a factory as “minimum wage” types? 
You seem to be missing the crucial detail of the HPT and the reason inspection is performed after it. Saying the test and inspection process “don’t mean shit” to quality control in rifle production is certainly not an indication of someone who is enlightened. Again, that crap belongs on TOS.
Yes, MPI can resolve near subsurface defects but they may never be seen or can be overlooked. The minimum size of a defect that can be detected is dependent on many factors such as:
- AC or DC magnetization; AC is generally used for surface detection only. DC can reveal subsurface defects by a well trained technician as many subsurface indications may appear diffused at best.
- Dry particles or Wet suspension; Dry particles are larger and therefore detection sensitivity is less than that of particles suspended in liquid. Particles in wet suspension are generally 10 times smaller than their dry counterpart.
- Visible or Fluorescent particles; Contrast is the key to detection. While it is generally accepted that Fluorescent is more sensitive to smaller defects, many times bright machined parts can be hard to interpret due to glare from part shine and liquid carrier when wet method is used.
- Excessive or Insufficient Amperage; Proper calculations are required to determine correct amperage for given part shape, size, length, diameter, material, etc.
- Inspection Speed; The longer the technician has to inspect the part under current, the better chance of defect detection. Current retention varies for different materials, therefore longer current holds may be needed. Manuf/Prod line inspection is often hurried, giving the tech insufficient time for complete and thorough inspections.
- Technician attitude, fatigue, insufficient training.
There are several more variables that could be listed, but as you can see there is way more to it than just applying current and throwing some ferrous powder across the part.
I don’t know what type of MPI is used on various firearm components or what the TDP mandates, but just saying a part has been MPI’d doesn’t guarantee a part to be defect free. A properly written procedure by someone whom not only knows NDT but also has some basic metallurgical knowledge of different steels along with their inherent tendencies to certain defects is certainly a key in developing a procedure capable of detecting critical flaws.
Anybody have any idea if the TDP either mandates or even suggests a given method? Anybody can buy a $700 AC yoke MPI kit and stamp MPI on parts all day long without having properly inspected them. A properly setup horiz. wet bench can run in the 10s of Ks range and when many manufacturers are making cuts, I often see these cuts in the QC/Inspection departments.
Those are good points, and yes, the testing is only as good as the procedure and the people executing it. Still, having the components undergo the prescribed high-pressure test prior to inspection, it is more effective than simply doing MPI alone.
I believe the benefits of having the bolt undergo a HPT followed by MPI are worthwhile, regardless of any doubts the community may have about the effectiveness or relevance of this testing process. The bottom line is that it increases the chance that a defective component will be identified and prevented from making it into a customer’s hands. Given the critical nature of a bolt, I can’t imagine why anyone would rather not have their bolt tested in this manner. Some cite the reduction in usable life of the bolt due to HPT, but it’s a compromise I readily accept.
I don’t frame my peers as minimum wage types, I’m just sayin’ what a job at an MPI station in a manufacturing facility pays (a little more than minimum wage but not much). And no, I did not make a career of performing MPIs.
I’m not missing any details, sjc3081 was one who said a bolt that failed in 500 rounds surely was not an MPI bolt. That’s not a valid statement. The bolt was MPI’d 500 rounds ago. That’s where I said [that] MPI don’t mean shit now.
I’m not saying that the testing/inspection process is worthless, I’m saying that the MPI test doesn’t have anything to do with a bolt that cracked 500 rounds into it’s life. The HPT/MPI assures that the bolt was in good shape when it left the factory. It does not assure anything going forward into it’s service life, and as you mentioned, the HPT can be detrimental. Look at the bolt life thread. Nobody has a wild ass guess as to how long a bolt will last and they’re all MPI’d.
I’ve said in other threads that material, process and dimensional inspection is a lot more important than HPT/MPI and that’s where the emphasis on QC should be since that’s what makes the bolt.
Can we please stop with all the MPI back and forth attacks and focus on the subject which is this crappy company that sells crappy parts? This should serve as a reminder that it is best to get parts from known vendors and companies.
I thought we were supposed to contact the company first… We seem to treat some companies differently around here.
I’m posting this to inform about a company hat sells MPI marked bolts that fail after 500 rounds of mild Wolf. The is a informational post. I don’t care about the company resolving the issue, I wouldnt buy their crap, and why I buy BCM first.
Oh I get it now, this is a PSA. If someone just wanted to let everyone know they got a crooked FSB from some other company everyone would say the company probably sells shit all the time…right? Your talking about a bolt that is MPI marked and most likely NOT made by the company that sold it. If you bought this bolt from a company well liked on this site this would have been shut down pretty quick. All I’m saying is we let this slide when it’s not the companies we love. When well liked companies do even worse stuff than this we act offended and ask “how dare you say these things in public without telling the company first and give them a chance to take care of it”. When we do it we sound snobby and hypocritical.
Nothing against you personally, but what if you contacting Sota and letting them know saved a “bad batch” of bolts from a good manufacturer from getting out there? You never know. On the other they could be intentionally selling shit as this post and all the replies suggests right?
I remember when I had no idea what kind of roaches were in the gun industry! 
On the other they could be intentionally selling shit as this post and all the replies suggests right?
Infinitely more likely. Bottom feeders like this can either just replace what breaks and please the idiots who bought it… or follow the Olympic Arms model and tell all their customers to pound sand when their garbage breaks.
Incredibly… the Olympic Arms business model works because their fanboys DO NOT want to think they bought crap… and thus defend the product to the death on the forums… and then cheap bastards talk themselves into taking the gamble too.
…I need to start a junk gun company. 
Good idea. Put out a competitively priced shitty product with a “lifetime guarantee” that you have no intention of honoring. Rake in profits till you get a bad name change company names and repeat as necessary.
Oly has never had to change their name. All they do is claim tighter tollerances than everyone else. They’re like the Obama of gun companies. Spin the story into the exact opposite of the truth.
I hope they at least have a guarantee.
Lifetime, of course.