Headspace & datum to case head

[Kramerica]

1.When setting up dies the datum line to case head measurement is the same as headspace? Headspace being measured with hornady headspace gauge. Is that correct?
2. Fired case measured with hornady headspace gauge measures 2.1425. Sized case measures 2.1440. Is that normal? The web, neck, below shoulder all got bumped down smaller by .002-.004”. So that headspace measurement is the only one that grew.

 

[RegionRat]

When setting up dies to size a case shoulder datum length, you can choose to target the cartridge specs, or to target a clearance to your particular chamber.

These measurements can be done as an absolute when the tools are "referenced" or "calibrated" to a real headspace gage, or just comparatively when referenced to your own samples.

The Hornady Headspace Comparator tools, are technically not the same thing as a headspace gage, but that is just being technical.

Those Horandy tools can be used to help set dies and control the shoulder datum length of the cartridge case.

 

[Coyotefurharvester]

The Hornady comparator is for comparing brass before and after firing. Before and after sizing. Because the tool(comparator body) is unlikely to contact the case in the correct position for actually measuring headspace relative to the chamber shoulder.

 

[jackieschmidt]

I have seen Threads with 100 post discussing just exactly what is meant by headspace.
RegionRat in post #2 is correct.

That being said, if you ask most shooters loading at the range “how much headspace are you giving your rounds”? they will know exactly what you are asking.

 

[FeMan]

In answer to question #2, as brass is being sized the compression squeezes the case and will push the shoulder forward, until the shoulder contacts the die and then starts to get "bumped" back. It sounds like you have begun the process but need to run the brass still deeper to get the shoulder bumped back.

 

[BoydAllen]

The Hornady tool is a caomparitor. Its name is misleading. You have a couple of correct answers to which I will add that if you are sizing once fired brass, it is unlikely that it needs bumping. How does the sized case fit in the rifle? BTW do you know the reason that we bump?

 

[Oso]

If your measurement as determined by the Hornady Comparator has increased from the fired case from your rifle to after resizing the fired case through FL Sizing Die then one of two things has happened:
(1) The Fired Case was not yet fully formed to match your rifle's chamber, which usually takes 3 firings to expand to match your chamber.
(2) If Fired Case that has been used 3x times through your rifle's chamber then your rifle's chamber is materially different than the FL Sizing Die's dimensions.

How do you determine which one it might be.... drop the resized case into your rifle's chamber and close the bolt. Does it easily close? If so then your rifle's chamber is still longer than the resized fired case. Assuming the rifle's chamber is not cut shorter than standard die's dimensions, you should expect additional case lengthening at the shoulder until the fired case has fully expanded to match chamber..

 

[Kramerica]

let me clear up that this is my fathers semi-auto hunting rifle (30-06). Using small base die. 1x fired factory federal ammo.

@Coyotefurharvester that is exactly how I was using the gauge ( before and after firing and then again before and after sizing). I’m just still not grasping how the my web sized down .002: behind the shoulder got sized down .005; neck ID got .007. But measurement I took using the hornady comparator headspace gauge grew .0015”. Is that normal? Safe to load? Or do I need to screw die down in more? Or is that measurement supposed to grow after being sized? Similar to how the case length grows while after sizing.
@RegionRat so the measurement with the hornady comparator should be called shoulder datum to case head? They just muddied the water by calling it a headspace gauge, which could be confused with a go/ no go gauge.
@BoydAllen I’d like to set up this particular die to work across multiple rifles and firings without messing with the die to much after initial setup if possible. I’ll take a shot at your question, We shoulder bump so there is clearance, so the round will chamber correctly, to avoid pressure and stuck cases? Also the sized case chambered and extracted just fine.

 

[59FLH]

-“I’d like to set up this particular die to work across multiple rifles and firings without messing with the die to much after initial setup if possible”-

Your will need to bump to your shortest chamber or use the mfg recommended instructions for set up.

 

[Kracken McGraw]

But measurement I took using the hornady comparator headspace gauge grew .0015”. Is that normal? Safe to load? Or do I need to screw die down in more? Or is that measurement supposed to grow after being sized? Similar to how the case length grows while after sizing.

Take FeMan advise above. Size it to at least the same measure on the comparator that you got on fired brass. I would go a half thousandth to a thousandth more than that.

 

[Kramerica]

-“I’d like to set up this particular die to work across multiple rifles and firings without messing with the die to much after initial setup if possible”-

Your will need to bump to your shortest chamber or use the mfg recommended instructions for set up.

well I’m already there. 1/4 turn clockwise after ram and shell holder contact sizer…
Kinda waiting on the other questions I posted to get answered to clear up the confusion on my part before I proceed

 

[fkimble@charter.net]

I'lll tackle the shoulder growing part. There used to be an auto commercial. They used a weiner shaped balloon. It had lines separating the words, down payment, monthly payment, interest. The idea was if you squeezed the word down payment , the other words got bigger. In other words something had to give. Squeeze the case sides down, the case length gets longer because the shoulder is not yet contained by the die. Also the small based die is squeezing the base even more than a regular die. Auto loaders don't always need a small base die. The fact that the shoulder length gets longer tells us that die is not down enough to contact the shoulder in the die. Will that longer case still chamber easily ? If so shoot that case again and check shoulder length again before sizing.

To use one die for several different guns, you need to fined the smallest chamber and set the die up for it. That will be your "factory" brass. Small enough to fit any gun. Case life will suffer when the brass is fired in the other guns with longer chambers. Chamber sizes will determine how much. Remember to fire a couple cases in each gun 3 times, resizing only the neck. Take your measurements and adjust the die. For factory hunting rifles this should work fine.

Frank

 

[59FLH]

All length measurements increase as diameters are decreased until the shoulder contacts the die, then lengths start to decrease as the die is lowered. “Screwed down more”

Safe? Yes

Normal? yes

Diameters don’t grow, only lengths.

Take a clay cylinder and roll it between your hands and a table, diameter gets smaller as length gets longer.

Hornady does not call it a Head Space Gauge it called a Headspace Comparator. No confusion it compares before against after,

Shoulder bump aka resize is so cases chamber.

I hope this info is helpful

 

[Kramerica]

Alright I got that shoulder to case head dimension to size down -0.0015. But it cams over pretty hard. As alluded to before probably because it’s a small base die? And I don’t need a small base die for this particular chamber I’m assuming. Web grew by .001 but is still .001 under fired brass dimension. Behind shoulder stayed the same.

 

[JFrank]

Can you draw out the cartridge and fill in the before and after sizing numbers prior to shaving the shell holder a couple thousandths ?

 

[Kramerica]

Can you draw out the cartridge and fill in the before and after sizing numbers prior to shaving the shell holder a couple thousandths ?

I can barley draw a stick figure. I can just give you the measurements I took though if you want? I didnt shave the shell holder I just kept Turing the die down to see what would happen. It finally sized but it cams pretty hard

 

[JFrank]

Can you trace around a case ?
shaving a shell holder a couple k takes about a half minute on a belt sander

 

[Kramerica]

Can you trace around a case ?
shaving a shell holder a couple k takes about a half minute on a belt sander

Here’s what I ended up with. This is without shaving the shell holder. Again cams over pretty hard. So I’m thinking of getting a non small base die.

 

[K22]

Lots of good answer here - just will add - Remember - the only reason cases are sized is so they will properly fit the rifle chamber without over sizing and hold a bullet with sufficient bullet tension.

Various bump gauges are used to aid in setting up the sizing die. They are used as a comparative tool to determine the amount of shoulder set back from a fired case to that which has been sized. The datum line provides a reference point for this comparison. Using gauges provides a comparative quantitative measurement.

Before there were gauges, experienced shooters / reloaders use the rifle chamber as a gauge to assess if the sizing was sufficient. The difficulty with this method is that it requires some experience to assess the proper "feel" of the sized case being chambered thus this process is more qualitative than quantitative. With that said, it has been my experience that the rifle chamber is the ultimate gauge to determine if the case is sized properly and by extension to set up the sizing die. So, a spot check is always a good idea in my opinion to check you gauging process.

 

[philip brousseau]

If you want to use a sizing die for multiple rifles get the Redding competition shell holders and make note of which shell holder bumps to correct length and always size with hard jam between shell holder and die bottom. No die adjustment necessary.