rem 740 742 barrel conversion

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billmech

Plastic

Joined

Apr 3, 2018

• Apr 5, 2018

• #1

Another project i have, 740 Rem 30-06.
Has anyone done this before? How is the head space set? Original barrel has bulge, to cut would make it less than 16". All parts are in nice condition and action moves smooth.

Thanks, Bill

 

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maynah

Stainless

Joined

Mar 24, 2005

Location

Maine

• Apr 5, 2018

• #2

Bill, I might have a 740 barrel in '06 kickin around.
I'll have a look.

 

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billmech

Plastic

Joined

Apr 3, 2018

• Apr 5, 2018

• #3

Ok, thanks

 

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BobbyBailey

Aluminum

Joined

Nov 7, 2010

Location

upper southwest Arkansas,USA

• Apr 5, 2018

• #4

Bill, a short barrel can be saved by making a flash hider / extension to get it past 16". If the hider/extension is pinned and welded over the pin it is okay. We have saved a few like this for guys not wanting to spend for a new barel and fitting.
On the headspace for 740/742, it is set pretty much same as any other. The barrel extension is fitted kinda like the extension on an AR. Except the extension on the 740/742 is a bugger to get off and requires the making of a wrench fitted to the extension.

 

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billmech

Plastic

Joined

Apr 3, 2018

• Apr 6, 2018

• #5

BobbyBaily,
So the barrel will detach from the recoil lug?

I can make a tool to remove bolt lock extension.
To me, it looks like the bolt locking extension must maintain a certain position?

Bill

 

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BobbyBailey

Aluminum

Joined

Nov 7, 2010

Location

upper southwest Arkansas,USA

• Apr 6, 2018

• #6

Bill, the barel extension is threaded onto the barrel, locking the lug in place between the barrel shoulder and the extension. The extension does have to have alignment with the gas block, lug, ect.. The extensions are kinda thin and can be cracked if not supported right. They are easiest to remove by making a relief cut in the barrel just ahead of the lug.
It will be way easier to locate another 740 barrel or to legally extend your barrel than it is to rebarrel yours, though if you are looking for a project, it will make one for sure !

 

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billmech

Plastic

Joined

Apr 3, 2018

• Apr 9, 2018

• #7

BobbyBaily,
I have read that I can convert this 740 to have a 742 barrel and 742 breech bolt.
Is it possible and is it a direct fit.. headspacing must be checked, of course..

from your last post, looks like the recoil lug is a separate item?
I'm up to the challenge to save this masterpiece. It was my fathers and it handles great in the woods.


Thanks again, Bill

 

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BobbyBailey

Aluminum

Joined

Nov 7, 2010

Location

upper southwest Arkansas,USA

• Apr 9, 2018

• #8

Bill,
It has been a while since I've had a 740 in the shop but, going of of memory I do think you could covert it to a 742 barrel with a 742 bolt. Ideally it would be great if you got a barrel with the matching bolt.

Yes, the lug is a separate piece.

 

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billmech

Plastic

Joined

Apr 3, 2018

• Apr 10, 2018

• #9

BobbyBaily,
If you don't mind answering, I have one more question/clarification from above on headspacing.

"On the headspace for 740/742, it is set pretty much same as any other."
Is this adjustable somehow? I'm not familiar with AR.
If headspace is to close, i can ream the chamber deeper.
If to far, i dont see how to get it closer.

Thanks, Bill

 

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BobbyBailey

Aluminum

Joined

Nov 7, 2010

Location

upper southwest Arkansas,USA

• Apr 10, 2018

• #10

Bill, I don't mind answering questions. Helping is what its about.
Maybe using this analogy will help; Look at or treat the extension as if it is a receiver on a Rem 700 bolt action. The barrel screws into the receiver with the lug between the barrel and the receiver. With the 740/742, the barrel screws into the extension with the lug between the barrel and the extension.
They headspace basically the same way. On a 700 the measurements are taken with the bolt in the receiver. With the 740/742, the measurements are taken with the bolt in the extension.
If the headspace is too great, you set the barrel back just as with a 700. The trouble with setting back an existing barrel is the gas block and gas hole. On a new blank, you would attach the gas block and drill the hole after everything else is good

If I made that as clear as mud, don't be afraid to say so.

 

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billmech

Plastic

Joined

Apr 3, 2018

• Apr 11, 2018

• #11

No mud, except here in maine.
So if I buy a used 740 barrel, I need to get one with matching bolt?
Otherwise i may not be able to get headspace set correctly?
It Doesn’t appear there is anyway to close the headspace after the gas block is attached.

And how is the gas block removed, if I decide to go that route. I’m trying to weigh my options and I don’t want to buy a used barrel I can’t use.

Thanks, bill

 

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BobbyBailey

Aluminum

Joined

Nov 7, 2010

Location

upper southwest Arkansas,USA

• Apr 12, 2018

• #12

Getting the matching bolt makes it all easier. If you are looking at gun shows, take a go gauge and some shims cut to fit the head of the guage to make sure the fit of the bolt. Or use a no-go and shims. Shims of .001 can be easily stacked on the bolt face , held in place by a tiny bit of grease.
We have had switched bolts when a bolt cracked and have had trouble with headspace on only one, that one was just too loose.
I think the barrel thread is 20tpi, not positive. CRS, you know LOL. But at that, setting the barrel back one turn would only be 0.050 to the rear. If 16tpi it would set back 0.0625.
Either of these amounts should still work, may need a little milling from gas cylinder. Probably not though.
The gas block is silver brazed to the barrel and would be best to mill the barrel from off of your gas block. Take the cuts slowly and lightly and you will see just how it was attached. That will answer some other questions.LOL
Having it tig welded on could be another good way to attach and might be a little better for heat management. The bore will need to be protected from scaling.

Bobby

 

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billmech

Plastic

Joined

Apr 3, 2018

• Apr 12, 2018

• #13

Bobby,
Ihank you very much for your input. I appreciate all the help.
I'm going to keep looking for a 740 barrel or a 742 barrel/breech lug. 742 barrels seem to be much more common to buy.
I may cut and add an extension and see how it works, but like to get it back to original length.

I need to finish the thompson venture project first as their recoil lug has a very large chamfer and moved & bent around a bit.

Thanks, Bill

 

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billmech

Plastic

Joined

Apr 3, 2018

• Apr 25, 2018

• #14

Quick update, i have now have a 742 barrel and 742 parts bolt on its way.