9310/QPQ, A better Bolt?

[jerrysimons]

I made it.

well the guys here made it.
It's the bolt going in our adjustable carrier.
They are single operation milled in an 8-Axis Turn-Mill

9310
Heat treated
Cryo process
MPI
And QPQ'd



I only have 2000 rounds on my test carrier, I can check it out tomorrow and see what the extension looks like. I have been focused on the carrier.

[Junkie]

That's a lot of bolts.

Regarding MPI, do you do a high pressure test first? I've seen claims that without one it's much less effective (it could be very soft or very brittle but not have cracked yet as it hasn't been loaded).

[redmist]

I don't have the means to do HPT. So we simply do MPI... Is it needed??? Probably not.

I think at the stage they are in during MPI, it's more of a check for flaws in the material after machining.


I still fully believe the machining process contributes the most to the lugs that crack next to the extractor pocket. That nasty undercut you see on some bolts from poor machining is a perfect stress riser in that area....

I am talking about this here: the bolt on the right has a very commonly found undercut from driving around the back of the lug at the .45

[BufordTJustice]

I don't have the means to do HPT. So we simply do MPI... Is it needed??? Probably not.

I think at the stage they are in during MPI, it's more of a check for flaws in the material after machining.


I still fully believe the machining process contributes the most to the lugs that crack next to the extractor pocket. That nasty undercut you see on some bolts from poor machining is a perfect stress riser in that area....

I am talking about this here: the bolt on the right has a very commonly found undercut from driving around the back of the lug at the .45

I think the speed at which these bolts are machined would also play a part in how much stress is introduced to the steel during machining. Making a better bolt may cost more simply because it must be machined more slowly.

[nova3930]

I know in general 9310 is considered to have good impact and fatigue properties. I couldn't tell you how it compares to C158 though. Probably take a lot of time and $ to know for sure how they compare. Just as a SWAG though, I'd bet that 9310 with the QPQ surface treatment probably produces a pretty robust bolt...

[Junkie]

Do many bolts fail MPI?

I figure that, absent HPT, you could probably make the bolts out of 1020 and they'd still pass MPI.

[tom12.7]

There's some things to be said about crashing the car before you buy it to make sure it's safe. I don't believe that HP testing of all bolts is needed. I would be more interested selecting a quantity from a batch, then HP test them to destruction and observe the results. I would rather not buy a car that has been crashed, I would rather buy a car that tends to do well in crashes.

Edit, because I can't type well to save my life.

[ColtSeavers]

I don't think the ARP bolts are QPQ nitride treated - I think they are just phosphate coated. I could be wrong, but I have two and they don't look like QPQ.

I recently picked up an AIM 9310 QPQ bolt out of curiosity. It looks pretty. Haven't used it yet. I am wondering if a nitride treated bolt is likely to wear out the lug area of the barrel extension faster than a phosphate coated bolt would.

My apologies, I was always under the impression that they were melonited as well just like the barrels.

[constructor]

The only broken bolts of this type that I remember reading about were a bad batch from ARPerformance ones that Harrison quickly either replaced or pulled from circulation awhile ago. If memory serves, it was a bad heat treat that was the culprit. Apologies as I do not personally have any experience with them though.

I do have a 9310 phosphate bolt in my frankenbeater with around 2k rounds on it though that so far has been performing just fine if that helps at all.

Very old thread found during search but...I have never Nitride or Melonite treated the bolts that we machine. I had a batch of inexpensive 5.56 bolts that came from toolcraft that I returned.
From my experience with Melonite treated barrel extensions I think it is a bad idea to Nitride treat bolts or extensions. Carriers are not subjected to impact force so Nitride treated carriers should be safe.