Headspace Explained

Doublezranch

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I found this article on headspace and thought I’d post. This gives pictures along with some high level explanations. Enjoy!

 

J E Custom

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Proper Head space is the heart of any accurate rifle. Proper loading is the part that maintains this head space. One is the Smiths/assemblers responsibility, and the other is the re loaders.

J E CUSTOM
 

Mram10us

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Proper Head space is the heart of any accurate rifle. Proper loading is the part that maintains this head space. One is the Smiths/assemblers responsibility, and the other is the re loaders.

J E CUSTOM
I'm curious what you mean. Are you saying there is a set headspace number, regardless of reloading for the .002" bump, as an example, that makes them shoot better?
 

J E Custom

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Yes. Each gunsmith has his or her own head space recommendation/belief based on the use and need of the firearm. Head space ranges from .0000 to ,0015 for the accuracy minded and .002 to .004 for function priority. .006 or .007 normally become the rejection head space that may become dangerous.

In many cases while fire forming, -.004 to -.006 crush (Less than .0000 head space) is advantageous to hold the case firmly in position while it is formed.

These dimensions have nothing to do with sizing the cases more or less than the chamber size, because this is regulated by the Re-loader. and is at his control and preference.

Fire arms are not head spaced to automatically add shoulder bump or any other dimensional need or belief, it is set at a standard best suited for the service and maintained by the re loader.

My beliefs on how much head space is best for the use is based on my experiences and may be different than some others based on there experiences. But ether way, head space is fixed once the chamber is cut and head spaced is set. The correct head space definitely has a bearing on the total performance of a firearm.

After the head space is set, the re loader has total control of how much clearance or head space he will have dimensionaly from the set head space and chamber dimensions. This is also the owners time to alter the locked in head space if it is not what he wanted or not ideal for his use.

J E CUSTOM
 

Mram10us

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Thanks. When you say 0-.0015, is that from the beginning of the saami spec range or go gauge?
 

rammac

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I'm not clairvoyant but I'd bet he's saying .0000" to .0015" relative to the chamber's headspace dimension.

Obviously you can make headspace anything you want, as long as the case and the chamber are within a couple of thousandths of eachother. The problem is that if you stray too far from the SAAMI or CIP specs then you're eventually going to have to design a new set of dies - I'm pretty sure that that's what they call a wildcat cartridge and chamber.
 

J E Custom

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Thanks. When you say 0-.0015, is that from the beginning of the saami spec range or go gauge?


Go gauges are the Minimum that SAMMI recognizes, To be within SAMMI Specification, the bolt has to close on the go gauge, so the go gauge would set the head space as .0000 if it will allow the bolt to close with no clearance between the gauge and the bolt.

I like to add shims for the needed head space to the back of the go gauge to set head space exactly what I want it to end up. The type of cartridge has a bearing on the amount also. With the head space set, I can shoot factory ammo or load fire formed cases that have Zero head space if desired with no movement of the case and no compression (bolt in battery has no movement when fired), and shoot them in the same chamber.

J E CUSTOM
 

Mram10us

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Go gauges are the Minimum that SAMMI recognizes, To be within SAMMI Specification, the bolt has to close on the go gauge, so the go gauge would set the head space as .0000 if it will allow the bolt to close with no clearance between the gauge and the bolt.

I like to add shims for the needed head space to the back of the go gauge to set head space exactly what I want it to end up. The type of cartridge has a bearing on the amount also. With the head space set, I can shoot factory ammo or load fire formed cases that have Zero head space if desired with no movement of the case and no compression (bolt in battery has no movement when fired), and shoot them in the same chamber.

J E CUSTOM
From my understanding talking to JGS, the go gauge is not the low value listed on the chamber diagram with the .010” range. They all differ a bit. That’s why I asked. So you are going off of the go gauge then. Thanks

edit: JGS uses the low value on the saami spec for their go gauge. Not sure about all others
 
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Mram10us

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I'm not clairvoyant but I'd bet he's saying .0000" to .0015" relative to the chamber's headspace dimension.

Obviously you can make headspace anything you want, as long as the case and the chamber are within a couple of thousandths of eachother. The problem is that if you stray too far from the SAAMI or CIP specs then you're eventually going to have to design a new set of dies - I'm pretty sure that that's what they call a wildcat cartridge and chamber.
See why I asked? I might have read it wrong but seems like JE is going off the go gauge

edit: seems that all go gauge manufacturers make their go gauge based on min saami spec.
 
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Doozy

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I had no idea there was such thing as a .001" shim. I just looked it up on amazon, and sure enough...

In another month I'm going to put together my first gun (a hunting rifle in 300 PRC) which is why I thought I'd browse the gunsmithing posts. It is Savage-shanked barrel/action. I bought a Go and No-Go gauge from Dave Manson Reamers. Now I'm wondering if I need to add a shim to my Go gauge. Is this something you would recommend @J E Custom? If so, do you have a recommendation on the thickness (if this is a proprietary secret, then I withdraw my question; I'm innocently ignorant in this area of gunsmithing).
 

J E Custom

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I had no idea there was such thing as a .001" shim. I just looked it up on amazon, and sure enough...

In another month I'm going to put together my first gun (a hunting rifle in 300 PRC) which is why I thought I'd browse the gunsmithing posts. It is Savage-shanked barrel/action. I bought a Go and No-Go gauge from Dave Manson Reamers. Now I'm wondering if I need to add a shim to my Go gauge. Is this something you would recommend @J E Custom? If so, do you have a recommendation on the thickness (if this is a proprietary secret, then I withdraw my question; I'm innocently ignorant in this area of gunsmithing).


The go gauge is to set the head space to SAMMI minimum for Sammi chambers and commercial ammo use. you can actually set head space tighter that the go gauge for wildcats that require fire forming, but I would recommend the go gauge plus .001 or .002 shims added. this would allow you to shoot factory ammo and then if you wanted to load for the rifle the head space can be adjusted for the head space you want or need with the loading dies.

The way I set head space is .0005 to .0015 depending on the use and if the person reloads.
For gas operated firearms I use .0015 to .003. for self defense, I will go to .004 (The bolt may close on the no go gauge) at this head space but again adding a .001 thousandths shim to the no go gauge should assure that you don't have .005 and be in a range that is not recommended.

I don't use no go gauges simply because I wan't to know exactly what head space I have and the shimming method gives me exact dimensions instead of a range somewhere between .000 to .004

This is done by setting the head space with the go gauge to where it will close with just the weight of the bolt or slight finger pressure. Then to reach the exact head space I'm trying for, I add the appropriate shim to the back of the go gauge. normally if you develop the "Feel", the slight feel as the bolt closes is near .000 to .0005 so if I add a .001 shim to the back of the go gauge, it will be .0015. the way you can check this is to insert a .002 shim in place of the .001 and the bolt doesn't want to close. (Don't force any chamber gauge closed). just to be sure you can try your no go gauge and it shouldn't close at all.

Field gauges are designed to warn you that the chamber is loose and not recommend for use (They are normally .006 to .008)

You can buy brass shim stock in small rolls in dimensions from .001 up and I have a supply up to .020. that comes in handy for other uses.

Hope this helps

J E CUSTOM
 

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