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Discussion Starter #1
Guys-

I'm making a couple of bolt heads and carriers for a one-off project and was just wondering if I could get some input on the heat treating done to the parts. And what metal is used for the parts. Price and machine time really doesn't matter in this case.

Thanks!

Mit Matelske
 

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If price doesn't matter then why not use OEM new german stuff? What you are wanting to do is no small feat for a hobbiest. OR a major manufacturer for that matter.
 

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Check out the chart on page 17 of this study. I believe it will get you in the right ballpark as far as metallurgy and heat treatment:
Trunnion Survey - Further Analysis - Page 17
We have been using 9310 for the last 4 years on all of our parts. Your chart is correct except we do use a carburizing block on the area of the pin hole inside and in both counter bored areas. And we have found the 9310 to be a better choice for caburizing. We ask for max hardness .025-030 deep
 

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Guys-

Price ... really doesn't matter in this case.

Thanks!

Mit Matelske
I'm wondering why you don't just modify an existing bolt and carrier to match whatever caliber you are secretly trying to cook up? Especially since price doesn't matter. Myself and my bud make all sorts of strange one offs also, but being cheap bastages, we start from scratch and spend no jing... and he gets paid to do "research"...
 

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Discussion Starter #6
We have been using 9310 for the last 4 years on all of our parts. Your chart is correct except we do use a carburizing block on the area of the pin hole inside and in both counter bored areas. And we have found the 9310 to be a better choice for caburizing. We ask for max hardness .025-030 deep
The thread on militaryfirearm.com is extremely interesting, but I'm not sure if it is applicable unless bolts and carriers get the same heat treatment as trunnions. I'm assuming from 75bronco's response they do.

Thanks guys!

Mit Matelske
 

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Discussion Starter #7
I'm making a small run of bullet guides to replace the cast ones SW uses. I'm running them out of 9310 based on feedback in this thread.

I'm wondering if I should heat treat them, or if the action of welding them in would just ruin any heat treatment anyway.

Thanks!

Mit Matelske
 

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Depends a lot on how close the weld will be to the wear surface too. Look at all the welds around a trunnion, yet they perform their functions well. The best thing would be to produce a sample then test the hardness after welding. A welded case-hardened part should still perform better than a soft one.
 

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The thread on militaryfirearm.com is extremely interesting, but I'm not sure if it is applicable unless bolts and carriers get the same heat treatment as trunnions. I'm assuming from 75bronco's response they do.

Thanks guys!

Mit Matelske
Not the same. Depends on the part and other factors.
Mike
MM
 

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Grand Chazzar
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Any "part " can be tested to determine what heat treat range they are in
Several different methods of doing so .
Most common , puts a dimple in the "part" & has an analog dial .
It's as easy as reading a clock .
Newer versions of Rockwell hardness testers don't even put a demple in the part .
 

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Newer versions of Rockwell hardness testers don't even put a demple in the part .
Could you point me to a site that shows this equipment? I thought I'd used about every method for hardness testing there is but I haven't run across this one yet. I may be able to use it here in the lab at work.
 

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Could you point me to a site that shows this equipment? I thought I'd used about every method for hardness testing there is but I haven't run across this one yet. I may be able to use it here in the lab at work.
They leve an impression but not a dimple .....
I've seen some that look like you used a pin punch ........
I have only used the dimple kind ...
My friend used one of the new ones that leves virtually no impression ....
I'll hit him up the next time I see him .
 

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For doing dept of hardness we do a cross section and then use a knoop micro hardness tester to test at various locations along the cross section. Note is 100% destructive testing ;-).

Can't link to my photos as they are behind the fire wall and did not use any in the Lab's website, but random line and photo of chrome plated case hardened (smaller indentation is harder material). Knoop Hardness Test Method | Newage Testing Instruments
 

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I don't recall anyone saying a Rockwell tester determined the type of heat treat .
As for the depth of hardening, different diamond indenters can be used to obtain readings for depth of hardening .
Also 2 tests are usually performed , the preload ( first indenter) , breaks thru thru the surface ,
Then the 2nd indenter , ( major load ) is done & held for a period of time to allow for any spring ,when released that position is measured against the position from the preload the difference is converted to a RH number , & can be used to obtain a depth of hardness as well .
 

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I mostly use Rockwell and Knoop and yeah, also have to do the section and polish routine for microhardness. As far as the reference to depth and type I'm not sure where that came from. In the Trunnion study I think Chasgee was using a combination of microhardness and dies for viewing the crystaline structure to determine depth. It's been too long ago for me to remember without going back and reading through it all again.

I'd be surprised if there was a big difference betwen the hardening methods used on a trunnion and a bolt head. I cross drilled a Cetme bolt head earlier this week and it was obviously softer in the core than it was on the surface, very similar to the trunnions we checked.
 
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