Did a search and couldn’t find any info on MPI tested bolts and barrels, sooooo…
What is it?
What does it do??
Do I want it???
Thanks!
All I know: its good and LMT does it, yes you want it. Probably someone here may ilustrate the tech details about MPI.
MPI stands for Magnetic Particle Inspection. It is a type of NDT process (Non-Destructive Testing) to check for flaws, cracks, etc in metal/conductive parts.
Basically, the part to be inspected is magnetized, and exposed to magnetic particles (either suspended in air or liquid), which are attracted to any cracks or fishures in the part. Any “reading” (high concentration of particle attraction) beyond nominal or acceptable limits and the part is usually disposed of. This may sound sort of vague, due to the fact that different parts have different acceptable standards, and different companies have different criteria for acceptance.
For example, there are small cracks that form at the base of the lugs on an M16 bolt after it is proof fired. The degree and location of these cracks is compared to the government inspection standard / quality assurance provision, which in turn determines whether the part is acceptable. Assuming the part is correctly proofed and then final-finished (phosphate), it is marked “MPI” to signify acceptance.
Hope this helps,
Clint
It is something you want in both your barrel and your bolts. To my knowledge, LMT, Colt and special ordered CMT (Stag Arms) are MPI tested.
For barrels, LMT, Colt and BCM are HPT and MPI tested. There maybe others, but I can’t think of any.
The thing to be careful of is that some companies MPI a couple barrels out of a batch, but go ahead and mark every barrel as being MPI tested (bad juju in my book).
The other big burning question is what are these companies exit criteria for a flawed barrel or bolt? I think some companies allow minor flaws in their products.
The only company I can say for sure that has a zero flaw acceptance policy is BCM.
C4
Interesting.
I win by the way.
For the necropost of the century?
I agree but if he didn’t do it IG would have canned the thread!
Pretty much. Or at a minimum the decade.
I can’t keep up with who does what, we need a chart! :sarcastic:
You can MPI any ferritic metal anytime you want. I’ve been MPI certified since 1998. I should start an MPI service for M4C.
I would even do a liquid penetrant for no extra charge!
Video explaining the process very well.
No cracks are allowed around the lugs or the bottom of the extractor slot around the lugs.
No cracks are allowed around the cam pin hole.
No cracks are allowed around the extractor pin hole.
No cracks are allowed on the face of the bolt.
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.
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Incidentally, MPI isn’t going to do much if done without HPT being done first…
The MPI doesn’t have anything to do with the HPT. Myself and some actual smart people think that the HPT does more harm than good pertaining to bolt life.
Remember, the MPI is only valid at the time of inspection. It’s just a method that allows a person to see some surface discontinuities easier. That’s it.
so you are suggesting that, if we had the time, facilities, and bolts to test, you would expect to see Colt and BCM bolts fail at a slightly increased rate when compared to bolts that do not undergo HPT? I hear where you are coming from, logically, but I’m skeptical. I just don’t think that people’s experiences over the years corroborate that point of view. Granted, i have no science to reference, but i think, over the decades, Colt bolts would have been exposed as slightly less reliable. Thats simply not the case.
I doubt that this has been tested on a wide enough scale say definitively one way or the other. A true test would require everything to be identical, with the exception of HPT, across a large number of guns.
Some high quality mfgs. are spec-ing bolts without the HPT. Apparently they believe there is a positive difference.
What is HPT?
High pressure test.
MPI and Dye tests are common in engine building machine shops, hell most industries where things might come apart under load. I might just take my bolts in and run the tests for shits and giggles. Would be an interesting sample test of 3…
The MPI would likely work ok, but the penetetrant (it’s penetrating oil) would likely make a mess in the phosphate finish.
You could clean your bolt and look at it with a magnifying glass and be real close to MPI. The real purpose of MPI is that it makes surface discontinuities easily viewable.
Don’t take my word for it. Ask Knights Armament about it…