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op rod steel?

This is a discussion on op rod steel? within the Gunsmithing forums, part of the M14 M1A Forum category; Anyone know what steel is used in the manufacture of USGI op rods? I need to weld a tab on and want to use a ...


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Old March 7th, 2017, 12:15 PM   #1
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op rod steel?

Anyone know what steel is used in the manufacture of USGI op rods? I need to weld a tab on and want to use a suitable match to make the the tab from.

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Old March 7th, 2017, 12:19 PM   #2
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That's a good question. I'm sure someone knows.

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Old March 7th, 2017, 12:24 PM   #3
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That's a good question. I'm sure someone knows.
Hmmm, that sounds like a Democrat answering a reporter's question....

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Old March 7th, 2017, 12:26 PM   #4
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Jerry K says 8645 steel for origional GI specs. Heat treated to RC40-46.

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Old March 7th, 2017, 02:19 PM   #5
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That is the correct spec, but I doubt if any of the op rod manufacturers are producing them with that steel. I know of one company who investigated the availability of this steel and was told that they would have to order about 20 tons to have it made up. That's a lot of op rods... I guess it is not a common specification.

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Old March 7th, 2017, 03:47 PM   #6
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Thanks for your replies.
I'm not sure where I could come up with a piece of 8645. Hopefully a piece of 4340, which I do have, will suffice. .

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Old March 7th, 2017, 06:53 PM   #7
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Thanks for your replies.
I'm not sure where I could come up with a piece of 8645. Hopefully a piece of 4340, which I do have, will suffice. .
8645 should to be heat treated after welding, so it would not be the best choice for a repair.

See if you can find some pre-heat treated steel.

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Old March 7th, 2017, 08:31 PM   #8
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I had Columbus Machine Work do a repair on one op-rod. Maybe contact them to inquire what filler rod they use?
http://www.columbusmachine.com/oprod.htm

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Old March 8th, 2017, 03:54 PM   #9
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I found a reference for the operating rod on the M1 Garand: Handle: 8645, 6150, or 8740 may be used. The tubing is seamless steel tubing: 1050. AFAIK all parts of the M14 op rod are supposed to be 8645. Op rods need to have a certain amount of spring to them so they can return to their original shape after cycling. Of course we all know that op rods do bend with use. Technicians who worked at Springfield Armory adjusting op rods were among the highest paid workers there.

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Old March 8th, 2017, 07:07 PM   #10
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I contacted Columbus Machine to see if they would give any advice. The email I got stated that they would not be willing to do anything other than listed on their site. They wouldn't even offer any advice on a suitable steel to use for making the tab. This is a very small tab that will be welded on the front right side to give the gas piston a flat surface to bear against on the SOPMOD. I don't think it needs to be particularly hard, just of a compatible steel to achieve a good weld.

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Old March 9th, 2017, 10:16 AM   #11
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I have had excellent results with tabs welded using 310 stainless. It doesn't accept a finish, but it doesn't show either. SS wear hardens so it holds up really well.

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Old March 9th, 2017, 04:38 PM   #12
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thanks Ted. I didn't know that I could weld stainless to carbon steel. I took a look in a reference book I had on hand and made the tab from a piece of 4340. I've always assumed that the op rods forward travel is slowed by the action of stripping the round from the mag and rotating/closing the bolt, I've never noticed any indications of hammering to the front of any of my op rods where they impact the gas piston. Do you think this might be a concern with 4340 ?

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