Why is it only AR bolts need to be MPI and HP tested?

dreadpirate · Nov 24, 2016

Everyone says you MUST get an AR bolt that has been magnetic particle inspected and high pressure tested. Ok - so why don't other semi-auto rifles required the same? I never hear of an AK, or a FAL, or a SCAR 17, or a G3 requiring these tests on their bolts. Why is that??

DaemonAssassin · Nov 24, 2016

Must be lore or old wives tales. But then again I could be wrong.

I'm just tagging because this piqued my interest.

mopar92 · Nov 24, 2016

It's part of the TDP for a mil spec rifle. To ensure the bolt is manufactured to specs and will be safe to use*.

The AK's, FAL's and G3's of the world may not require such stringent testing and proofing (although the G3 probably does)

*The MUST part is really perpetuated by those mil spec fanboys who masturbate over Matechs, carry handles, M855, and suffer from premature ejaculation when someone mentions Colt.

Post GWOT initiation and expiration of the Federal AWB the AR market has exploded with accesories and parts that fall into 3 categories, less than mil spec, equal to mil spec and better than milspec (application dependent)

Milspec is simply a STANDARD. It is up to the end user to determine what they need in a rifle.

Let's talk bolts. Bolts are made in batches and either not tested, batch tested or individually tested. Theoretically speaking if Company A makes them out of the same material and makes them the same way as Companies B and C there should be no issues providing there are no flaws in the raw material. Company A makes em doesn't test em just ships em out. Company B tests 5 out of every 100 made. Company C adheres to the milspec and tests every individual bolt. IF it where my money I would buy from company C for peace of mind.If I was given a rifle with a bolt from company B I wouldn't worry too much. If given a rifle with a bolt from Company A I'd probably send it to be tested if possible.

The most important thing is when you clean the gun to inspect the bolt for cracks, flaking, pitting, uneven wesr on the lugs, and discoloration EVERY time. Generally a good guideline is every 1k down the tube. Buy a spare bolt and enjoy life.

dreadpirate · Nov 24, 2016

Ok MOPAR - then based on what you just said, I would say the QC of the manufacturer is most important, and also that buying a bolt from a top notch company then is more important than a MILSPEC bolt from "Shit Guns R Us".

[EDIT - although I admit all of the top-notch companies seem to MPI/HPT their bolts]

TheBert · Nov 24, 2016

dreadpirate said:
Ok MOPAR - then based on what you just said, I would say the QC of the manufacturer is most important, and also that buying a bolt from a top notch company then is more important than a MILSPEC bolt from "Shit Guns R Us".

[EDIT - although I admit all of the top-notch companies seem to MPI/HPT their bolts]

How are you using the weapon? Is it a wall hanger? Is it a plinker? Is it a shooting range queen? Is it a "hunting" rifle? Is it a home defense weapon? Is it your SHTF weapon?

mopar92 · Nov 24, 2016

dreadpirate said:
Ok MOPAR - then based on what you just said, I would say the QC of the manufacturer is most important, and also that buying a bolt from a top notch company then is more important than a MILSPEC bolt from "Shit Guns R Us".

[EDIT - although I admit all of the top-notch companies seem to MPI/HPT their bolts]

All the top knotch companies got that way through excellent QC and in house manufacturing. I won't buy an AR part from a company that doesn't offer in house pinned front sight assemblies and mil spec bolts/BCG's. Those two items are the KEY to a reliable AR. Any retard with a machine shop can buy barrels and assemble guns with set screw gas blocks, can cut teeth off a barrel nut, and thread a barrel with a tap and die set. But those two items require fixtures, templates, jigs and testing facilities and it's a fair shot that if they can hold QC on those two items and make a profit then the chances go up on everything else.

dreadpirate · Nov 24, 2016

TheBert said:
How are you using the weapon? Is it a wall hanger? Is it a plinker? Is it a shooting range queen? Is it a "hunting" rifle? Is it a home defense weapon? Is it your SHTF weapon?

Good question. I would have a different attitude of I were a mercenary operating in some harsh corner of the globe. My (modern) firearms are mostly plinkers and hunters.

dreadpirate · Nov 24, 2016

Now I am wondering how many of my AR bolts are MPI/HPT. BCM bolts are; most (but not all) PSA bolts are; Remington (aka DPMS)??? Windham weaponry??? Anyways - all this has been very useful.

Biggfoot44 · Nov 24, 2016

IF Crap Guns are Us individually tested each bolt, then the consumers would be assured of getting at least a milspec bolt. The company might have a high internal rejection rate, but the ones that passed would be "milspec" .

If a high end boutique mfg with tight QC randomly picked a batch and didn't test them, they would have very high probability of being fine.

It would be in the middle, ie a company too new to have a track record, or has a so-so reputation, that does batch testing, where you would pause and make a decision.

Tracker · Nov 25, 2016

If you're not going to war buy what you can afford but PSAs MPI/HPT bolts are only a few bucks more than their non MPI/HPT ones. On my two builds I went with tested but that's just me.

outrider58 · Nov 25, 2016

dreadpirate said:
Ok MOPAR - then based on what you just said, I would say the QC of the manufacturer is most important, and also that buying a bolt from a top notch company then is more important than a MILSPEC bolt from "Shit Guns R Us".

[EDIT - although I admit all of the top-notch companies seem to MPI/HPT their bolts]

QC is a fluid term. Even the best manufacturers have bolts that fail the MPI testing. That's why the test. It is also probably due to the method in which AR/M4 bolts made.

Pinecone · Nov 25, 2016

How are AR bolts made?

A lot of the others are machined from forgings. So less likely to have issues.

outrider58 · Nov 25, 2016

Pinecone said:
How are AR bolts made?

A lot of the others are machined from forgings. So less likely to have issues.

Then why is there a need to test them? Probably because AR bolts are so massively produced that 'flaws' occur. That's my uneducated guess.

I'm throwing this in for edification:

https://www.nde-ed.org/EducationRes.../MagParticle/Introduction/basicprinciples.htm

iH8DemLibz · Nov 25, 2016

The AR bolt is a different animal when compared to most bolts.

There are eight little lugs. That means there are sixteen internal corners that can develop stress fractures during the manufacturing/forging and cooling stage. If you want to count the back side of each lug, that's eight more 90 degree corners.

Metal parts love failing/cracking where sharp corners are involved.

.02

dreadpirate · Nov 25, 2016

This is interesting, since I was always inclined to think the MPI/HPT was marketing hype. I did not realize it was part of the MILSPEC. Maybe it's a good $25 investment (or so of extra cost) for that extra bit of assurance.
[EDIT - sometimes only $5 difference]

dist1646 · Nov 25, 2016

A friend of mine thought he would save some money by buying a less than mil. spec. bolt. When one of the lugs next to the extractor broke off, it didn't turn out to be such a good deal. The lug next to the extractor cut seems to be where most of them fail. He replaced it with a mil spec bolt and hasn't had a problem since.

dreadpirate · Nov 25, 2016

Although not readily apparent from their website, looks like Windham Weaponry does MPI/HPT their bolts:

http://blog.cheaperthandirt.com/attention-detail-meticulous-craftsmanship-windham-weaponry-mpc-m4/

Pinecone · Nov 25, 2016

iH8DemLibz said:
The AR bolt is a different animal when compared to most bolts.

There are eight little lugs. That means there are sixteen internal corners that can develop stress fractures during the manufacturing/forging and cooling stage. If you want to count the back side of each lug, that's eight more 90 degree corners.

Metal parts love failing/cracking where sharp corners are involved.

.02

Are they forged? Or machined from cast?

Either way, that was my thinking, more likely to have issues based on how they are manufactured.

Also, the lugs are smaller, so a minor flaw could have big consequences. Versus an FAL bolt which is a pretty massive chuck of steel.

outrider58 · Nov 25, 2016

Pinecone said:
Are they forged? Or machined from cast?

Either way, that was my thinking, more likely to have issues based on how they are manufactured.

Milled from forgings.

Pinecone · Nov 26, 2016

Thanks. Less likely to have issues that machines from cast

Why is it only AR bolts need to be MPI and HP tested?

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