Signs of high pressure test?

[Disciple]

I bought a bolt that was advertised as Magnetic Particle Inspected and High Pressure Tested. I can see no evidence of this test. The bolt face and the front and back of the lugs appear pristine and there is no carbon on the bolt tail. Is this not as advertised or am I mistaken in the signs I expect to see?

[markm]

Some companies sample test a portion of a batch and still mark the whole lot HPMPI as I've read here before. I personally wouldn't worry if the manufacturer is otherwise reputable. I've only had off brand bolts break prematurely.

[lysander]

High Pressure testing can be done with hydraulics, cheaper and cleaner . . .

And even if done with a cartridge, since the test set-up has no relative motion, there will be no evidence of the testing.

[constructor]

I bought a bolt that was advertised as Magnetic Particle Inspected and High Pressure Tested. I can see no evidence of this test. The bolt face and the front and back of the lugs appear pristine and there is no carbon on the bolt tail. Is this not as advertised or am I mistaken in the signs I expect to see?

I've been trying to tell people for over 15 years the HPT is BS most of the time.

Manufacturers of bolts offer the MPI stamp for an extra dollar. The proof loads themselves cost $4 a shot so how do these companies mount barrels and bolts in a jig , fire a $4 test shot then inspect the bolt and barrel for $1 then stamp the bolt? They don't, they offer the stamp as a convenience service then it is up to the company manufacturing the firearms to test and discard bolts that do not pass. Back in the day Colt and FN were the only 2 companies that proof tested bolts and barrels.

Steel today is much better than it was back in the 60s and 70s, as long as manufacturers don't cut corners and use 8620 the steel should not have impurities that will effect the strength. IMO the heat treat used by the manufacturers will be more critical than quality of the alloy.

[Disciple]

High Pressure testing can be done with hydraulics, cheaper and cleaner . . .

And even if done with a cartridge, since the test set-up has no relative motion, there will be no evidence of the testing.

That's a revelation. I don't know if this could honestly be desdribed as "proof fired" however which I think it also says. I'll have to check.

I've been trying to tell people for over 15 years the HPT is BS most of the time.

...

Steel today is much better than it was back in the 60s and 70s, as long as manufacturers don't cut corners and use 8620 the steel should not have impurities that will effect the strength. IMO the heat treat used by the manufacturers will be more critical than quality of the alloy.

In this article Mike Mihalski of SOLGW states "People don’t realize that with well-made 158 carpenter steel bolts, about 3 percent of them will fail the HP test." This is what put the on the path of wanting an individually HP tested bolt. If HP testing can actually be had do you think it is of value?

[constructor]

That's a revelation. I don't know if this could honestly be desdribed as "proof fired" however which I think it also says. I'll have to check.





In this article Mike Mihalski of SOLGW states "People don’t realize that with well-made 158 carpenter steel bolts, about 3 percent of them will fail the HP test." This is what put the on the path of wanting an individually HP tested bolt. If HP testing can actually be had do you think it is of value?

Sure...IF they really have been tested.
I've never found a company that can prove they have been tested. Each bolt would need a serial number and a video of the test along with proof the ammo had been certified at a certain pressure. In the end it comes down to trust, who do you trust?
I tested the bolts I machined, at first all of them but after none were found to have cracks from MPI I started batch testing. I had Hornady make the proof loads for me which should have been 74000PSI. A short while later I called and asked Hornady for the data sheet on the loads, it said 92000psi and the testing was for 6.8 bolts which should be tested at a lower pressure than 5.56 bolts.
I stopped machining 5.56 bolts after doing a bunch of hyd destruction tests, I compared the bolts I was machining to Microbest bolts and both were well over the test limits. I've sold tens of thousands of 5.56 Microbest bolts over a period of 14 years and never had one break.

[Disciple]

That's very different from "about 3 percent of them will fail" and I don't to how to reconcile it. Are you presently selling Microbest bolts?

[constructor]

That's very different from "about 3 percent of them will fail" and I don't to how to reconcile it. Are you presently selling Microbest bolts?

I retired in 2017. Blackstone Arms is taking over my business including my Microbest account. After he gets the 5.56 products going he will sell Microbest bolts.

In all fairness I think the guy was saying 3% of some bolts that are high pressure tested will fail the MPI, not "will fail and break in the rifle". We don't know what type/brand of bolts he was referring to. Microbest will not make Grendel bolts and SOLGW sells Grendel bolts so...who makes them and do they also use the same brand 5.56 bolts?
I've never used SOLGW and they have a VERY limited description of their bolts. https://sonsoflibertygw.com/shop/solgwbolt556158c/

[lysander]

That's a revelation. I don't know if this could honestly be desdribed as "proof fired" however which I think it also says. I'll have to check.

If they aren't using hydraulics to test bolts, bolt makers are going about testing in a costly and inefficient manner.

With a bolt, the only thing you are worried about is the thrust load from the cartridge, the bolt really can't tell if that thrust comes from the firing of a test cartridge, or a pulse from a hydraulic ram . . .

[T2C]

If they aren't using hydraulics to test bolts, bolt makers are going about testing in a costly and inefficient manner.

With a bolt, the only thing you are worried about is the thrust load from the cartridge, the bolt really can't tell if that thrust comes from the firing of a test cartridge, or a pulse from a hydraulic ram . . .

That makes sense. Would a hydraulic test jig be faster than using a proof cartridge jig? I am guessing the answer is yes.

In manufacturing, saved time is profit.