C158 Bolts vs. MPI

[lysander]

Really. I've always stuck to Colt and BCM because they are trusted brands. I picked up a PSA pistol with KAK brace on a whim and noticed the bolt markings. I never have gotten much into material specs and whatnot.

I realize PSA is probably a B-grade fireaarm. I just don't want it to be a Z-grade firearm.

Battlefield Las Vegas seem s to be pleased with the life they are getting out of PSA uppers (with PSA bolts)

[SteveL]

Another thing to consider with regard to HP testing is the specs of the HP test round used. As I recall there is a spec for that test round. The reason I bring it up is because back in the days of "the chart" there was one company in particular, and I'm 99% sure it was DD, who did HP testing, but they did it with their own test load and not the same test load everyone else used. That makes me wonder if some of these cheaper brands who claim they do HP testing are doing the same HP testing as everyone else.

[everready73]

Another thing to consider with regard to HP testing is the specs of the HP test round used. As I recall there is a spec for that test round. The reason I bring it up is because back in the days of "the chart" there was one company in particular, and I'm 99% sure it was DD, who did HP testing, but they did it with their own test load and not the same test load everyone else used. That makes me wonder if some of these cheaper brands who claim they do HP testing are doing the same HP testing as everyone else.

This as well as the fact that companies like BCM and colt HPT test and MPI every bolt. Many of the mid to lower grade companies only batch test and still mark the bolts. It is hard to tell if the bolt you bought was actually tested or just a couple out of a large quantity.

To be fair to PSA Henderson defense has a long running thread on TOS and they run very high round counts on the PSA bcg's. They said they last as long as expected I believe 20k or so rounds. I do believe they said the colt bolts do outlast them but going off memory. I only have one PSA bolt with a few k rounds

I do think there are other important factors other than specs and testing between brands. Even if a PSA premium etc bolt has the same specs as BCM/colt there are brands out there that use mim extractors and crap extractor springs

I think a good quality/price compromise is Sionics Milspec BCG. It is $120 and C158 hpt/MPI with a sprinco extractor spring. SOLGW have went up in price the last year or so but Primary arms runs sales for $115 and they are a good value at that price.

[tehpwnag3]

Let's face it. Without certification, just about any unscrupulous company can buy a laser engraver and mark bolts with it. There, I said it.

[MistWolf]

What's being overlooked is shot peening. Proper shot peening is important to prevent early bolt failure.

[26 Inf]

This as well as the fact that companies like BCM and colt HPT test and MPI every bolt. Many of the mid to lower grade companies only batch test and still mark the bolts. It is hard to tell if the bolt you bought was actually tested or just a couple out of a large quantity.

There are, as you know, several differing views on HPT.

In the one camp there are those that say that the HPT severely reduces the finite number of pressure spikes that the bolt will withstand. (I about typed that the HPT 'exceeds what the bolt is designed to withstand' but that isn't actually true, the bolt is designed to withstand the HPT. That is this guy's stance:

The idea that HPT decreases the expected life of a part is bunk. The part is DESIGNED to take the load that the HPT delivers. If it is properly designed and manufactured it will take that load literally an infinite number of times before failing. It's called "infinite life calculations" in engineering.

I should have added the following caveat: I haven't seen the design calculations for an M16 bolt. I don't even know exactly what pressure an HPT round is loaded to.........I only speak from my experience as a registered Professional Engineer.

Knight's is perhaps the best known adherent to the HPT testing shortens bolt life, and they seem to have done okay for themselves engineering and production-wise.

What I think would be a winner is batch testing random bolts from each differing lot of alloy. This would reveal any flaws in that lot's manufacture. Myself, I'd hold those bolts back and not sell them. All bolts would be MPI'ed.

My cars have airbags, they weren't crashed before I bought them; likewise my truck wasn't dropped to ensure the suspension could withstand rough roads. Suffice to say, I know that at least one vehicle was crashed, and another dropped, to ensure the durability.

I don't see why bolts would be any different, except, because, you know, 1950's-60's knowledge and technology.

[SwampYankee]

I though Carpenter 158 was the mil spec steel specified. MPI is a good thing but you do know that KAC believes that firing a high pressure round during testing shortens bolt life by up to 50%. They don't proof their bolts and warranty them for I believe 22,000 rounds.

That was my understanding of c158 as well. Also I believe Centurion arms is of the same opinion as KAC about the proof testing. That's why I don't think I really care about only buying hpt bolts anymore.

[Todd.K]

The idea that HPT decreases the expected life of a part is bunk. The part is DESIGNED to take the load that the HPT delivers. If it is properly designed and manufactured it will take that load literally an infinite number of times before failing. It's called "infinite life calculations" in engineering.

I should have added the following caveat: I haven't seen the design calculations for an M16 bolt. I don't even know exactly what pressure an HPT round is loaded to.........I only speak from my experience as a registered Professional Engineer.

This is a great example of where book smarts gets engineers into trouble. The 5.56 didn't exist when the M16 was developed, so it's quite flawed to assume the bolt was engineered for the HP of a round that didn't exist.

[Doc Safari]

Battlefield Las Vegas seem s to be pleased with the life they are getting out of PSA uppers (with PSA bolts)

Good point. I had forgotten about that. The results surprised me. Nothing offers proof better than destructive testing.

I just love these technical discussions. You get a gazillion opposing opinions and all of them supportable--but nothing beats actual 'testing to destruction.'

[ChattanoogaPhil]

The HendersonDefense thread is one of the more interesting threads on the Net.

HPT/MPI... Over the years I've seen much discussion on the subject but what I haven't seen is an authoritative source cite rejection rates for any manufacture or materials. Does such information publicly exist beyond hearsay?