Chamber headspace gauges and Case Length gauges

[SteveW-II]

Am I correct in believing that a chamber headspace 'GO' gauge represents the maximum headspace dimension that ammunition should be assembled with ?

Remember, I am talking about 2 different things here. Chamber headspace and the length of the brass case on the headspace dimension.

Whenever I have headspaced a chamber, I have worked on the guidance that the bolt should close on a 'GO' gauge and not close on a 'NO GO' gauge. So imagine that WHILE I am reaming the chamber, the bolt will not close on a GO gauge until I have cut down to the gauges headspace length. Now the bolt will just close on the GO gauge. The bolt will not close on a No Go. So, I am done.

In fact, the bolt will not close on ANY gauge longer than a 'GO' gauge. My chamber is now exactly the same headspace length as the GO gauge.

Now, I expect any 'in spec' ammo to fit in that chamber.
Am I right or wrong ?

I ask because I dropped a headspace 'GO' gauge into a Lyman case length gauge yesterday. I was surprised to see that the GO gauge was below the 'max size' point on the case gauge. That means that if I dropped a re-sized brass case into the case gauge, even if the brass case was longer (in the headspace dimension) than the GO gauge, I would still think that it was correctly resized. I am sure that it would not correctly chamber in some of the guns I have built, however.

Are the chambers I have cut correct or incorrect, or is the case gauge incorrect ? Maybe this is a gunsmithing question..

Puzzled of Austin.

 

[Bart B.]

You're right.

I think the specs for ammo, .308 Win. for example, is that case headspace (head to shoulder datum) should be between 2 and 5 thousandths less than the GO chamber headspace gage of 1.630-inch. This lets all (correctly made) factory ammo chamber properly and safely in that chamber.

All of my match rifles in .308 Win. are reamed such that chamber headspace is about 1.6305-inch so the bolt'll just close on a 1.6300-inch GO gage. I put a borrowed 1.6310-inch gage in two of them and their bolts wouldn't close with the weight of the bolt handle being the only pressure on the bolt to close it. Best accuracy with all new rimless bottleneck cases happens with this chambering technique.

Are you talking about the Lyman gage shown in in the link below?

http://www.lymanproducts.com/lyman/case-prep/ezee-case-gauge.php

 

[SteveW-II]

> Are you talking about the chamber headspace GO gage you
> dropped in the Lyman case length gage had its head below
> the MAX surface at the back/top end of the case length gage?

Correct. 1.6300" GO chamber headspace gauge dropped into a Lyman 308 case gauge has it's head below the MAX surface.

 

[SteveW-II]

Case gauge as in : http://www.midwayusa.com/viewProduct/?productnumber=271313

Couldn't see it on the Lyman site.

 

[Bart B.]

Steve, you responded to my first post while I was editing it. Oops!!!

But anyway, if your .308 GO chamber headspace gage stops in the Lyman gage with its head below the max flat, that's fine. The MAX flat is probably 1.634-inch; the dimension of the NOGO .308 Win. headspace gage.

There's typically a couple thousandths spread across many of these gages intended to measure cartridge cases. As long as your chambers won't let the bolt close on a NOGO gage but just easily close on a GO gage, your're good to go.

 

[SteveW-II]

Thanks. That at least means I can rest easy about the chambers I have cut !

Edited to say that I went back and checked again. Using the 'Go' gauge in the case gauge,
a straight edge and some small feeler gauges told me that there was a gap of 1.5 thou
between the top of the headspace gauge and the top of the case gauge.
Just sayin' !

 

[kelbro]

How does the no-go gauge fit in the case length gauge?

 

[SteveW-II]

> How does the no-go gauge fit in the case length gauge?

Sticks out of the top of the case gauge by 3 thou.

 

[Clark]

Bart B.?
THE Bart B.?

You have resurfaced on the internet on THR?
I try to read every word you ever post.

 

[SteveW-II]

As another fascinating tidbit, I put my 308 'GO' chamber headspace gauge into my RCBS 308 precision mic today. The mic said that the headspace gauge is 1.5 thou smaller than '0'. Sooo, than means that I have been cutting chambers that might be about one thou 'tight'.

However, if - as Bart B. mentions (post #2), the ammo spec is that the headspace dimension is one to two thou less than the chamber gauge, then all is good.

 

[USSR]

Am I correct in believing that a chamber headspace 'GO' gauge represents the maximum headspace dimension that ammunition should be assembled with ?

No. Case headspace dimensions should be determined by your particular rifle's chamber headspace dimension, since chamber dimensions vary from one rifle to the next. Assuming you have a .308 rifle with minimum chamber headspace dimensions (1.6310"), then your case headspace dimension for a bolt action rifle should be 1.6290" (.002" less than chamber), and either 1.6270" or 1.6280" (.003" - .004" less than chamber) for an autoloader. Since most factory rifles don't have such tight chambers, the case headspace dimensions for a factory rifle is likely to be longer.

Don

 

[SteveW-II]

Don, I am sure that's true for handloads.

However, my (badly worded) question boiled down to : Are factory rounds sized to fit inside a chamber cut to close on a 'GO' gauge, and nothing larger ? I think that answer is yes.

However, once fired in the chamber, the handloader can adjust the headspace to anything smaller then the fired brass.

 

[USSR]

Most factory .308 ammo case headspace dimensions are about 1.6280". The factorys don't know if their ammo will be fed to an autoloader or to a custom built rifle with minimum headspace. They are only concerned that their cartridges feed in all platforms.

Don

 

[Bart B.]

SteveW-II's question:

Are factory rounds sized to fit inside a chamber cut to close on a 'GO' gauge, and nothing larger ? I think that answer is yes.

No.

They range from about 1.625 to 1.629 inch new case headspace (on those I've measured) and will fit any chamber with headspace greater than 1.629 inch. Why? They're shorter in all instances; SAAMI minimum (GO) is 1.630, max (NO-GO) is 1.634. The (FIELD) danger one is almost 1.640; way too long for normal safety issues.

USSR's comments are right on; new ammo's gotta fit 'em all.

 

[SteveW-II]

I am not trying to pick a fight or anything, but if factory rounds :

> range from about 1.625 to 1.629 inch

And a :

> SAAMI minimum (GO) is 1.630

Then the answer to my question :

> Are factory rounds sized to fit inside a chamber cut to close on a 'GO' gauge

Is yes.

 

[Afy]

Bart B.?
THE Bart B.?
You have resurfaced on the internet on THR?
I try to read every word you ever post.

Clark pray elucidate....

 

[Clark]

Afy
Quote:
Bart B.?
THE Bart B.?
You have resurfaced on the internet on THR?
I try to read every word you ever post.
Clark pray elucidate....

http://groups.google.com/group/rec.guns/browse_thread/thread/88bef3bfe724b497/dcd9a8bf2c3f8c52

Leafing through my copy of the May 1997 issue of Precision Shooting, I
encountered an ad for Krieger Barrels, Inc. that showed an actual-size
copy of a 20-shot group shot at 800 yards by "Bert Bobbit

They didn't spell his name right.

 

[Sunray]

A case length guage has nothing to do with headspace. A case length guage only tells you if the case length is within spec. Has absolutely nothing to do with headspace.
Headspace is a rifle manufacturing tolerance only. It's what allows ammo of different manufacture to be fired, safely, out of all like chambered firearms. Cartridges, reloaded or factory, do not have headspace.
When you install a new barrel or bolt, you MUST use proper headspace guages for the cartridge. The bolt should close on a 'Go' guage, but not on a 'No-Go'. However, if it does close on a 'No-Go', try a 'Field'. If the bolt closes on a 'Field' guage, the headspace is excessive and the rifle is unsafe to shoot with any ammo.
A 'Go' guage is minimum tolerance. A 'No-Go' is high, but not excessive. A 'Field' is max headspace.

 

[SteveW-II]

Sunray, did you read the thread ? I don't think so.

 

[USSR]

SteveW-II,

Sunray is a denier of the connection between case dimension and chamber dimension in regards to headspace, even though many manufacturer's and retailers specifically sell tools to determine "case headspace" dimensions.

Don

 

[AR-15Nutt]

In fact, the bolt will not close on ANY gauge longer than a 'GO' gauge.

this statement is totally incorrect

i have had the BCG close and lock on NIB Colt, Bushmasters and LWRCI guns, with the "NO-GO" gauges, the best and only gauge i use is the "Mil-Spec Field Gauge", as recommended by my Military Armorer buddy.

 

[Clark]

Quote:
In fact, the bolt will not close on ANY gauge longer than a 'GO' gauge.
this statement is totally incorrect

i have had the BCG close and lock on NIB Colt, Bushmasters and LWRCI guns, with the "NO-GO" gauges, the best and only gauge i use is the "Mil-Spec Field Gauge", as recommended by my Military Armorer buddy.

There may be difference between 1) how to optimally re-barrel a rifle and 2) when to consider a rifle not safe to fire with factory ammo.

 

[SteveW-II]

>> In fact, the bolt will not close on ANY gauge longer than a 'GO' gauge.

>this statement is totally incorrect

The context of my statement was for rifle chambers that I had cut on a lathe with a reamer and a 'GO' gauge to tell me when to stop. In those cases, my statement is 100% correct.

If you use rifles that will close on a 'no go' gauge but will not close on a 'field' gauge, then I think it likely that the only adverse effect will be that if you reload the brass, you won't get many reloads out of each case. You might also get light primer strikes.

I do understand that an auto loader may have a looser chamber than a bolt action. However, I bet that factory ammunition is sized to fit the chamber for the 'GO' dimensions.

 

[kelbro]

I set my bolt-gun barrels to close slightly snug on a go gauge and the bolt handle to go less than halfway down on a no-go gauge. Brass lasts a long time.