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This is a discussion on New bolt within the Gus Fisher forums, part of the Gun Professionals category; Gus, I just had my bolt replaced by SA due to the bolt roller coming off when I was cleaning my rifle at the end ...


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Old November 14th, 2012, 10:53 AM   #1
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New bolt

Gus,
I just had my bolt replaced by SA due to the bolt roller coming off when I was cleaning my rifle at the end of the season (no elbow grease, it just came off)SA requested that I send the upper receiver to them for repair due to warranty issues. When I got my rifle back they replace the entire bolt and the head space is now 1.1631.

My concerns:
I picked up some WWC from 1968 and was wondering if this would be ok to shoot through my gun now? I only ask because you and mention in previous post that NATO ammo shot a little faster about 150-200fps faster. It was linked ammo, does that make a difference?
Is this going to cause problems in the long run if shooting the WCC and switching to differant ammo/loads?
Thanks for the advice.

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Old November 14th, 2012, 04:43 PM   #2
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If it's M80 ball ammo it's what the doc ordered.

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Old November 14th, 2012, 11:42 PM   #3
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Quote:
Originally Posted by MickeyD1120 View Post
Gus,
I just had my bolt replaced by SA due to the bolt roller coming off when I was cleaning my rifle at the end of the season (no elbow grease, it just came off)SA requested that I send the upper receiver to them for repair due to warranty issues. When I got my rifle back they replace the entire bolt and the head space is now 1.1631.

My concerns:
I picked up some WWC from 1968 and was wondering if this would be ok to shoot through my gun now? I only ask because you and mention in previous post that NATO ammo shot a little faster about 150-200fps faster. It was linked ammo, does that make a difference?
Is this going to cause problems in the long run if shooting the WCC and switching to differant ammo/loads?
Thanks for the advice.
If there is not a tight NM chamber, I would not be concerned about firing a couple rounds to see how they work. Then fire trhee rounds fast. If that works, then you should be OK.

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Old November 15th, 2012, 02:36 AM   #4
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I've looked a this thread a few times now and no one has mentioned, but surely the OP really meant 1.631 (vs.1.1631).

Thanks from stoky
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Old November 15th, 2012, 07:17 AM   #5
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Headspace, chamber vs cartridge

While most discussions surrounding headspace address chamber or barrel headspace most discussions leave out cartridge headspace. They are not the same and are the cause of most of the misunderstanding about the interchangeability and safety of 308 vs 7.62x51.
The difference of the chamber or barrel to bolt headspace (available space for a cartridge to fit into) has been debated many times, the answer given has been it is safe to shoot 7.62x51 nato in a 308 chamber and the headspace of 1.630-1.632 is safe as there is no difference between nato and 308 rounds. Another argument presented has been "show me a 7.62x51 reloading die".
If you understand the difference between chamber headspace and cartridge headspace than this discussion is moot, if you don't than realize the average cartridge headspace for 7.62x51 nato rounds is 1.6315 while the average cartridge headspace for 308 is 1.630. These dimensions are the standards set by the governing bodies which are not the same organization.
SOOO what does it matter? In the past I have posted what I set chamber headspace at and why, I try to always set chamber headspace at 1.633-1.634, the reason is it sets the clearance for the cartridge to the chamber using the average cartridge headspace at between .0015 and .0025.
This clearance allows for safe chambering of the cartridge of both 308 and 7.62x51. If the chamber dimension is set at or below 1.6315 and you fire 7.62x51 nato rounds the average tolerance will not be a problem (it means you can say "well I have shot nato spec ammo for years and never had a problem") but, and this is where the rubber meets the road, if you shot 7.62x51 nato spec ammo and you get rounds that exceed the average cartridge headspace dimension but are still within nato spec of cartridge headspace dimension you can have an out of battery discharge, this can be where the bolt is mostly locked or where the bolt is mostly unlocked but it can be a real disaster if it happens.
If a rifle is headspaced at or below 1.6325 and the shooter wants to shoot either 7.62 nato or 308 ammo, I recommend he check his ammo through a cartridge headspace gauge that is set at .001 below the chamber dimension. If you look at the standards for either round you will see the maximum cartridge headspace for both is 1.633 which is .001 below the 1.634 maximum or even with the dimensions I select for chamber headspace. The only difference is the average vs maximum. This means there can be an interference fit of .001-.003 depending on chamber headspace set to 308 standards, an object larger than the provided space can not occupy it.
I consider a chamber in an M14 or M1A SET AT 1.632 OR BELOW to be unsafe for 7.62x51 ammo, yes many people and untold rounds have been fired safely from weapons set at these dimensions, but, and here is the very big but, if you run into 7.62x51 rounds that exceed the 7.62x51 average cartridge headspace but still meet maximum standards and your chamber headspace is below this dimension you can have a very bad day.

Jim

For a link to a fairly good discussion try this:
http://carnival.saysuncle.com/002453.html


Barrel or chamber headspace dimensions for:
7.62x51mm NATO Go 1.6355"
7.62x51mm NATO Field Reject 1.6455"

.308 Winchester Go 1.630"
.308 Winchester No Go 1.634"
.308 Winchester Field Reject 1.638"

Cartridge headspace dimensions for:
7.62x51mm NATO minimum cartridge headspace 1.630
7.62x51mm NATO maximum cartridge headspace 1.633
7.62x51mm NATO average cartridge headspace 1.6315

.308 Winchester minimum cartridge headspace 1.627
.308 Winchester maximum cartridge headspace 1.633
.308 Winchester average cartridge headspace 1.630

As you can see there's a notable difference between the headspace of the .308 Winchester & the 7.62x51mm NATO chambers. To put it in a more direct contrast:

7.62x51mm NATO Go 1.6355"
.308 Winchester Go 1.630"

That's a difference of .0055"

7.62x51mm NATO Field Reject 1.6455"
.308 Winchester Field Reject 1.638"


Where the real problem lies is in the cartridge headspace tolerances:

7.62x51mm NATO minimum cartridge headspace 1.630"
.308 Winchester minimum cartridge headspace 1.627"

7.62x51mm NATO maximum cartridge headspace 1.633"
.308 Winchester maximum cartridge headspace 1.633"

7.62x51mm NATO average cartridge headspace 1.6315"
.308 Winchester average cartridge headspace 1.630"

Thanks from budster
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Old November 15th, 2012, 10:13 AM   #6
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Quote:
Originally Posted by DavidinMD View Post
I've looked a this thread a few times now and no one has mentioned, but surely the OP really meant 1.631 (vs.1.1631).
DavidinMD, Thanks for pointing that out your right it should be 1.631

I think you all answered my question.
Thanks.

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