SAAMI head space dimensions- 3006 ?

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06shooter

New member
2.0487 min. 2.0587 max.
Factory cases are below min.- 2.042
I understand about auto loaders , levers etc....
Wouldn't SAAMI min. be for auto loaders etc.
I would like to fully understand this before setting up my FL die.
I get a measurement of 2.042 on new factory brass.
and I have read to set the shoulder back .002 " on fired brass , but what puzzles me is that my once fired brass is still 2.042" .
Since this measurement performs , would I not set my FL die to this ?

Why would I push the shoulder back .002" from what my measurement is from a factory case if the factory case is working ?
I don't mean to be troublesome , but I need to know before I move forward.

Isn't it bad to have it pushed too far back ? This concerns me , RCBS tells you how to set it , but when it chambers successfully, you really don't know what the distance is.

Thanks......
 
http://www.saami.org/PubResources/CC_Drawings/Rifle/30-06 Springfield.pdf

Chamber dimensions cover go-gage length to a no go-gage length chamber +.002. And the case does not have head space, it has a length that is measured from the datum to the head of the case.

SAAMI says: the case length from the datum to the head of the case could be 2.052 max and it could be .007" shorter, it could be anything between. SAAMI is not talking about you chamber, they are not talking about your cases. Your fired cases when measured from the datum to the head of the case should indicate the length of the chamber from the datum to the bolt face: Point? You have to decide if your going with SAAMI or your chamber.

I have measured factory ammo case length from the datum to the head of the case. I have been impressed, Factories have fewer problems sizing cases than reloaders.

F. Guffey

Isn't it bad to have it pushed too far back ? This concerns me , RCBS tells you how to set it , but when it chambers successfully, you really don't know what the distance is.
Click to expand...

'You really do not know'? Measure the case length from the datum to the case head of a fired case, after measuring you should know the length of the chamber from the shoulder to the bolt face. If you size the case and measure the length from the shoulder to the head of the case again you should know the difference in length between the case and chamber.

I start from the other direction, I measure the length of the chamber from the shoulder to the bolt face first.
 
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The measurements you are quoting (2.0487min.- 2.0587max.)
are for the chamber not the case
the case will go into the front of the bolt so the dimensions are
different
I am not sure what tools you are using to measure your case with
that is why I do not understand that measurement (2.042 )
some reloaders use a case gage or a case micrometer
with a case gage, you drop the case into it, then check to see if the case is between the two milled places on the gage (the case could be too long
(would be above the milled places))or too short (below the milled places )
a case micrometer measures the case length and will show if the case is too long or too short and how much it is over or short, in thousandths, indicating which way to adjust your die

most reloaders adjust the die by the manufacturers instructions
that will usually make the case too short, but the cartrige will chamber
and fire

I use the case micrometer ( comes in the RCBS, PRECISION MIC kit )

It boils down to how much you want to spend
cheapest-- manufactures instructions
modest investment-- easy to use and gives good check
more money-- exact measurement
 
Thanks again guys ,I'm using hornady's bushing and body comparator head space gauge.
Maybe I'm using too much pressure with my calipers . When I use them for case length ,primers etc.... it's good !

I'll study up on what you guys are saying , certainly my Weatherby s2 chamber isn't below min.

There is still the new factory case and the once fired case being the same size that has me cornfuzzled .

All the questions I have been asking and the answers here have been a BIG help !

Thanks again !
 
The Hornady gauge is not accurate enough to compare to SAAMI specs. It's just a hole in a piece of aluminium. A quick call to Hornady will confirm that the purpose of the gauge is to compare your fired brass to your sized brass, not to SAAMI specs.

Before Stoney Point (Hornady) came along we did it like this. It worked well, but it too could not be compared to SAAMI.

headspacegauge_zps59a89da2.jpg
 
If you want your Hornady gauge to read correctly, you'll need to calibrate it with a .30-06 chamber headspace gauge. Measure that head space gauge, then zero your caliper so it reads 2.049" with the gauge. Exact measurement is 2.0487" which rounds out to 2.049". Or zero it on the headspace gauge then used the readings as plus or minus values from 2.049" which is what the chamber gauge is.

Use the following for referene:

http://www.saami.org/PubResources/CC_Drawings/Rifle/30-06 Springfield.pdf

That Hornady gauge is not designed to give exact numbers, it's just a tool to compare case headspace from its fired condition to its resized condition.

Regarding the new factory case and the once fired case being the same size. That can happen with reduced loads. If loads are reduced too much, the fired case will have less headspace than a normal mzx loaded new case does. That happens as the case shoulder's set back a few thousandths from firing pin impact and if there's not enough pressure to stretch the case head back against the bolt face, the case headspace will be shorter. Primers are often seen sticking out past case heads when this happens.
 
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if your reloading and starting at a safe starting load and your micing the case head after firing then why does saami have to be an issue.

i know in some cartridges semi auto's have some slightly different dementions than bolt guns.but in those cases you can simply order the semi auto style brass.

im not sure where the problem is


my personal number 1 rule about guns.
only buy single shot or bolt guns never deal with levers or semi's for this very reason,they are more complex and a royal pain in the butt.revolvers are always better than semi hand guns too.

reloading is complex enough,dont deal with bogus guns that are not worth the advantages they may occasionaly have over bolt guns.
absolute reliabilty always rules over momentary convenience.

that is why they like doubles in africa,a guarentied second shot is better than a possible 3rd or fifth
 
Mr Bart , your comment about the new and once fired brass had me thinking about the powder and charge weight of that cartridge.
What I'm working with is a Remington scirocco 150 gr .
A while back I took this loaded round apart and weighed the charge , it was 54.0 grains of some type of ball powder.
I did the same thing with a 150 gr. Power shok, it weighed 57.0 grains , but I don't think I took a measurement on the shok case. It too was a ball powder.
Both of these are accurate ammo in my rifle. (Maybe this 54.0 gr. charge isn't pushing the shoulder enough ) ?

So what do you guys suggest in regards to what brand/ maker of a head space chamber gauge for a hunting rifle ?

Thanks guys , it's beginning to come together.
 
06Shooter, it's not important to get case measurements exactly when adjusting the sizing die in the press. The objective is to set the fired case neck back .002" and go with whatever that actual dimension from the case head to case shoulder reference diameter is. Therefore, you really don't need a chamber headspace gauge. Thousands of people resize fired cases very nicely without having one.

A popular solution to not sizing a case enough and it won't fit the chamber is to turn the die down 1/4 turn. That's way, way too big a step. One turn moves the die 1/14th inch; that's about .018 inch. 1/14th inch equals about .072 inch. Changing the die's position .018 inch may well be way too much.

Instead, turn the die in by moving a point on it about 1/10th inch in its circumference. That'll move the die up or down about .002 inch. Set the die so the case headspace is about .002 inch less than what the case was after firing and before sizing. There'll be a couple thousandths spread across all the cases so sized, so whatever die position sets the case shoulder back averaging .002 inch will do just fine.

Never ever guess what powder is in a loaded round unless you loaded it and knew what powder was used. Judging powder charges in a cartridge without knowing exactly what powder is in them is dangerous.

Again, your differences between a new case and its fired headspace being the same is easily explained. Your chamber is at SAAMI headspace minimum and the new case is close enough to it that when fired, it has the same dimension. I've seen that happen with a few new .308 Win cases whose headspace was 1,629 inch then after being fired in a chamber with 1.630 inch headspace, it was the same head to shoulder dimension; it shrank back from the chamber. You can get a good idea of your rifle chamber headspace by adding .001" to that of a fired case from it. But your gauge has to be calibrated to measure actual dimensions. Hornady's LNL bushings actually measure a few thousandths short; I think they caution users about that.

RCBS Precision Mic's are calibrated with a chamber headspace gauge, but they still may read a thousandth off when measuring one due to normal tolerances across them. SAAMI's spec's for the .30-06 chamber headspace gauge to be 2.049 + .0002 inch.
 
Thanks Mr Bart , what you said about the .308 example has to be what's going on.
Thanks for the very helpful info and to everyone else who has chimed in with their knowledge on reloading.
I will put this to good use !
 
So what do you guys suggest in regards to what brand/ maker of a head space chamber gauge for a hunting rifle ?
Click to expand...

I don't, I am the fan of standards, the head space gage is a standard and a transfer, problem, finding someone that understands what that means. There is also a no go-go gage. beyond that is the field reject gage. Another problem, everyone on this forum (with very few exceptions) could have ALL THREE AND STILL NOT BE ABLE TO DETERMINE THE LENGTH OF THE CHAMBER FROM THE SHOULDER TO THE bOLT FACE.

I measure the length of the chamber from the shoulder/datum to the bolt face in thousandths. Comparing? SAAMI specifications are nice, I can compare my dimensions with their case and chamber dimensions. My chamber, my cases and my dies with shell holders allow me to size cases to fit my chamber.

I have close to 600 rounds to load, I do not have access to the rifles, I only know the man that built them and ask me furnish the ammo. I know he started with factory ammo, I know the ammo he shot was/is accurate, and I know he does not have the same interest when cutting a chamber or sizing cases as I do. And, he has no interest in going with Ackley improved.

F. Guffey
 
to the person who asked about brass for semi autos.

im not sure what it is or how it differs.i have been told cases can be slightly different for semi autos and lever guns.i have never owned a semi auto or lever gun so i dont know.

i was just trying to understand the poster and what this thread might mean.i have never heard anyone care about saami specs on head space.if a case head has not expanded more than .0005 of and inch there should be no problem,if it expands more than that your over pressure most likely
 
The insert for the Hornady case comparator has the same hole diameter as the case shoulder datum, but because it is just aluminum and because a sharp corner would cut into the case, it has a slightly radiused edge around the hole that slips deeper over the case shoulder than the actual datum is. Where the shoulder actually touches the insert is the point the angle tangent to the radius matches the angle of the case shoulder. If the radius were precisely controlled, you could design the insert with a slightly undersized hole that would read correctly on a perfect case by actually touching a little bit high on its shoulder. But then it would only work on cartridges that had both the same datum diameter and the same shoulder angle. It would make the tool less versatile, so we settle for a little error and use the tool only for comparison and not for absolute measurements.

So, the only convenient way to know how to get close to an absolute measurement is to compare to a zero taken on a headspace gauge. Below shows using using a 3.8" ID journal bushing from the hardware store rather than the comparator adapter, but I am zeroing on a headspace gauge. Below that is an actual fired case being measured for comparison. Below that are a couple of .30-06 headspace gauges.

30_06gaugingheadspace1_zps4fe43de2.gif


30_06gaugingheadspace2_zpsc7a0184f.gif


30_06%20gauges_zpscdqw1jli.jpg


Note that as long as a case has been narrowed in a sizing die, it will usually feed well. Indeed, if you look at the SAAMI drawing, you'll see the maximum allowed "case headspace" is actually 0.0039" longer than the minimum allowed chamber headspace. This is because the case is enough narrower than the chamber that when a bolt closes on a 0.0039" longer case it has enough room to swell outward to accommodate the expansion due to that extra length. Closing the bolt compresses it and it doesn't take much force to do that. The reason it's hard to drive a case 0.0039" deeper into a full length sizing die is that the die is not only constraining the sides of the case, but is actually pressing them narrower, so you have the die trying to narrow and shorten the case simultaneously. That's why cases grow during resizing. Being squeezed from all directions flows brass into the neck.
 
if a case head has not expanded more than .0005 of and inch there should be no problem,if it expands more than that your over pressure most likely
Click to expand...

Before the Internet the case head expansion was .00025". The shooter used new factory over the counter ammo to get the reading. Then the question should be "What does the reloader do with the information?".

A reloader would use the factor once fired cases to check reloads. The reloader should expect no more case head expansion than .00025". The .0005" you have listed would be twice the amount of case head expansion for factory ammo.

The reloader could not expect to continue shooting and measuring and expecting .00025 case head expansion. The case head will work harden, logic would suggest a case head expansion of .001" could be expected after 4 firings.

I have tested receivers, I got wrecked case heads that would no longer hold a primer and the flash hole diameter could not be measured with my flash hole gage.

When the Internet came around it was decided no one was capable of measuring .00025" case head expansion.

F. Guffey
 
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@mr guffey

interesting,i had not heard that.


@O.P i think understand this post now.i had thought people were talking about case expantion but it appears were talking about chamber dementions

the way a rifle is chambered at factory and or by gunsmith cant be changed by the reloader.there is nothing a reloader can do to change case head lenth.if your NO GO gauge says your chamber dementions are off,then you must consult a gunsmith.the trick with the caliper using a flat wall and bottleneck together is rather dubious and risky.
 
Also note, that the diameter of the hole in the Comparator is not always the same as the SAAMI datum.

Take the 220 Swift for example, it has a SAAMI Datum measurement of .335, yet we use the Hornady .330 Comparator for this cartridge.

Other examples would be the 22-250 and the 300 Savage, they both have a SAAMI datum of .347 yet we use the .350 comparator.

There are several other examples were the SAAMI datum line is not the exact same diameter as the Hornady Comparator.

The Hornady gauge should be used to "Compare" your fired cases to your sized cases, not to SAAMI.
 
I just measured my Hornady gauge and it is at .372 instead of .375 " .
Click to expand...

Then there is the radius/beveled edge of the hole. It has never been necessary to purchases the gages for measuring case length from the shoulder to the case head. A reloader with shop skills can drill straight holes and use a height gage/dial caliper can manage to measure case length.

The hole: .372" or .375" and the question, how did you measure the hole?. Call RCBS and inform them you measure the inside diameter of one of their dies, they will ask you how did you measured the inside diameter of their die.

F. Guffey
 
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