9310/QPQ, A better Bolt?

[WS6]

Mil Spec extensions are 8620 that is heattreated (carburized) for a case harden.

9310 as used in bolts is typically also case hardened by carburizing.

According to the data sheets for 9310 the temperatures for SBN (1015 F) will anneal the core material and some yield strength will be lost.

But is that yield strength loss offset by the tougher surface? Most cracks begin in the surface of the rear of the lugs/fillets, or the cam-pin hole, and progress. Does the QPQ treatment help with this? Is the lower CoF of it in the barrel extension (real or theoretical?) help with the axial loading of the bolt lugs?

There is a lot more to consider aside ultimate yield strength.

I am not vouching for the above. I am simply posing the question(s).

[Cold/Bore]

There is a lot more to consider aside ultimate yield strength.

I agree. It would be nice (and cheeper) to be able to pit bolts of the various compositions and processes against each other and HPT them until failure and declare the last one standing the winner, but that won't really give you the real idea about which will last in a carbine. The variables of heat, fatigue life, friction and gauling, etc., are not accounted for.

[BufordTJustice]

I agree. It would be nice (and cheeper) to be able to pit bolts of the various compositions and processes against each other and HPT them until failure and declare the last one standing the winner, but that won't really give you the real idea about which will last in a carbine. The variables of heat, fatigue life, friction and gauling, etc., are not accounted for.

Yeah, fatigue life being there most complicated and interesting aspect to me.

Also, I wonder how cryogenic stress relieving/treatment, like they do for many automotive and commercial machine parts, would play into this bolt life equation as well. V7 Weapons offers a cryogenic treated C158 bolt in phosphate. Hmmmm.

[Clint]

Yep, that's the tough one.

Yeah, fatigue life being there most complicated and interesting aspect to me.

Cryo as part of an overal heat treatment plan is totally legit.

Specifically, using it as part of an extended quench before tempering, is solidly based in material science.

Some alloys can benefit and others don't.

Any quality heat treat company will be able to answer which is which.

Throwing all kinds of random purchased parts in the cryogenic treat is a waste of time.

Also, I wonder how cryogenic stress relieving/treatment, like they do for many automotive and commercial machine parts, would play into this bolt life equation as well. V7 Weapons offers a cryogenic treated C158 bolt in phosphate. Hmmmm.

[John_Burns]

But is that yield strength loss offset by the tougher surface? Most cracks begin in the surface of the rear of the lugs/fillets, or the cam-pin hole, and progress. Does the QPQ treatment help with this? Is the lower CoF of it in the barrel extension (real or theoretical?) help with the axial loading of the bolt lugs?

There is a lot more to consider aside ultimate yield strength.

I am not vouching for the above. I am simply posing the question(s).

Good question that are hard to find real solid answers.

The lugs that break actually break from a radial load during unlocking so a reduction in friction should help in theory.

[BufordTJustice]

Yep, that's the tough one.


Cryo as part of an overal heat treatment plan is totally legit.

Specifically, using it as part of an extended quench before tempering, is solidly based in material science.

Some alloys can benefit and others don't.

Any quality heat treat company will be able to answer which is which.

Throwing all kinds of random purchased parts in the cryogenic treat is a waste of time.

I owe you a phone call, bud. Got your voicemail. Been CRAZY busy on my end.

[MegademiC]

I tested a NIB bolt and the base metal on the lug was in the 50s Rc. I don't know if it was carpenter or 9310.

20s sounds way too low for an extension, but I'm a ChemE in the steel industry, not a metallurgist, so I could be wrong. We don't deal with ss much at all.

[redmist]

Yeah, fatigue life being there most complicated and interesting aspect to me.

Also, I wonder how cryogenic stress relieving/treatment, like they do for many automotive and commercial machine parts, would play into this bolt life equation as well. V7 Weapons offers a cryogenic treated C158 bolt in phosphate. Hmmmm.

I am currently running a 9310, Cryo'd, QPQ Bolt in my test carrier gun.

[jerrysimons]

I am currently running a 9310, Cryo'd, QPQ Bolt in my test carrier gun.

and where did you secure such a bolt?

[redmist]

and where did you secure such a bolt?

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.