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Discussion Starter #1
What makes a Mag partical inspection so critical for the AR bolt, and why do SO many people put so much weight in this inspection? It does nothing to strengthen the bolt. Is the manufacturing process of the AR Bolt that delicate that they need to perform an NDI of that single part for every rifle? I would guess its more of a quality control thing and I would like to know how many bolts get rejected from this in a given year from a manufacture. I bet it would be interesting to see the results.

The way I would see it, if you are that worried about your bolt shitting the bed why you would not peform an MPI every 3-5k rounds down range? Not just one initial NDI when the part is brand new. Being an aviation guy and having to deal with getting stuff NDI'ed with the various process of NDI, we dont perform one NDI inspection for the life of what ever part needs it. It gets a regular scheduled NDI inspection after so many calender days/flight hours/uses etc.

I guess I am just ranting, it seems like a marketing technique to me for the civilian rifle market. :beer:

Does any one know if the military performs regular NDI inspections on service rifle bolts after a certain amount of time in the field or round count? (I would assume it would be more of a calender type thing rather than round count)
 

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I think the process is that they fire a Proof round with the bolt...a over pressure round and then MPI the item and if it tests ok it is assumed good to go for service life with regular pressure rounds...kind of like how barrels are proofed...if they pass the proof load it is assumed they will last in normal service until they wear out with minimum risk of catastrophic failure. I understand that it is done more to detect unseen flaws in the steel stock that the parts were made from, not so much for finding or exposing manufacturing/machining errors. It also would help expose heat treat issues but mostly as i understand things it is largely to detect unseen flaws in the bar stock.
 

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Discussion Starter #3
BadBrad said:
I think the process is that they fire a Proof round with the bolt...a over pressure round and then MPI the item and if it tests ok it is assumed good to go for service life with regular pressure rounds...kind of like how barrels are proofed...if they pass the proof load it is assumed they will last in normal service until they wear out with minimum risk of catastrophic failure. I understand that it is done more to detect unseen flaws in the steel stock that the parts were made from, not so much for finding or exposing manufacturing/machining errors. It also would help expose heat treat issues but mostly as i understand things it is largely to detect unseen flaws in the bar stock.
I wasnt aware of the shooting an over pressure round then performing the MPI that makes alot more sense to me. Any MPI is done to detect unseen flaws or cracks in the metal or welds that cannot be seen by the naked eye. Thats what was throwing me off why NDI a that single part ONCE after the manufacturing process when in reality it should really be done over the entire life of the part till it either will not pass an inspection due to stress cracks or wears out or becomes unservicable. I know the average guy is not willing to have this done, unless they had access to an NDI lab and could get it done for fairly cheap.

Thanks for the info about the proof rounds, is the barrel proofed at the same time the bolt is?
 

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Doubt it as it could be two differant shops making the parts..one place making the bolt another the barrel
 

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Don't put too much weight in it. The percentage of bolts rejected during MPI testing is astronomically low...and the "main" reason it's done is to conform to a standard requested by the end user (aka...the military in most instances). It's become more of a marketing ploy now and I would have no hesitations using a non-MPI bolt. DO buy one from a reputable company though. And avoid the ones Midway sells under the name "AR-Stoner". They were being sold during the panic after Sandy Hook and QC was non-existent. That and they were likely not using the proper spec steel (158 Carpenter) as many people were complaining about peening and broken lugs after less than 100rnds.
 
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