Head Space

[Bret]

Easiest way to do it is to fire 5 or so factory rounds and measure them with a Hornady headspace comparator.
For gas guns, bump it back between .003 and .005.

+1
This has done the trick for me. I don't use mixed brass though, so I don't know if that would make a difference.

[purple bikerr]

I have a Hornady Headspace comparator, and all of my brass is PPU once fired. I measured approx. 100 pieces and they all sized to the same dimensions. But all the cases are right at 1.464". I do have to set my die back another .006.

[Bret]

The first thing that you need to understand about the Hornady comparator is that it does not provide an absolute headspace value. It simply provides differences between headspace measurements. Fortunately, you don't need an absolute headspace value, just the differences. If you were going to fire your reloaded ammo in multiple rifles or even rifles that you don't have fired cases from, it would be a good idea to resize it back to below the factory maximum size. However, you're not in that situation. You have one rifle that you need to size the cases for. You simply need to size them 0.004" to 0.005" below the fired case values that you're reading on your comparator. Any more than that and you're just overworking the cases for (in theory) less accuracy potential.

[markm]

If you were going to fire your reloaded ammo in multiple rifles or even rifles that you don't have fired cases from, it would be a good idea to resize it back to below the factory maximum size.

Exactly. I've always just set my die so that it averages in between the min/max on a head space gauge. I don't know why guys like to torture themselves with extra gadgets.

Even when setting up bolt gun dies, I simply use the gun as a gauge.

[T2C]

I have a Hornady Headspace comparator, and all of my brass is PPU once fired. I measured approx. 100 pieces and they all sized to the same dimensions. But all the cases are right at 1.464". I do have to set my die back another .006.

If possible, check the comparator with a chamber headspace gauge. After comparing the Stoney Point comparator with a 30-06 insert to chamber headspace gauges I discovered several thousandths of an inch difference. I logged the differences and take them into account when using the comparator.

Here are the readings I observed:

30-06 Headspace Gauge/ Stoney Point Measurement
Go --------2.0487”/ 2.041”
No Go – 2.0547” / 2.046”
Field ----2.0577”/ 2.049”

As others have recommended, it's a good idea to check resized brass with a cartridge headspace gauge. Until you have a cartridge headspace gauge, you can compare the headspace reading of resized brass with the headspace reading of brass on an unfired factory cartridge from a major ammunition company.

[eightmillimeter]

Plinking ammo? ... just set the die so the press handle cams over, don't even measure the headspace 'cause it just don't matter.

Trying to hold a 6 inch x ring in service rifle comps... then bump it back .003-.004.

[Eric D.]

That's bad advice. Depending on the dies and shell holder cam-over occurs at different places. If I set my Dillon sizing die up to cam over on the Rockchucker the brass would be sized back way too far to be even safe to shoot.

Plinking ammo? ... just set the die so the press handle cams over, don't even measure the headspace 'cause it just don't matter.

That Hornady comparator is a terrible tool to validate the measurements of headspace gauges. The inserts aren't bored accurately enough to take a reading from the established datum line on the case shoulder. They also tend to have radii that allow the insert to seat further down on the case shoulder than where the datum line is referenced resulting in shorter measurements as you observed. Someone above mentioned that tool isn't meant for absolute measurements but rather, relative ones where you use it to measure a fire-formed case and then a sized case and the difference between the two is what counts. Differences between true headspace values and what the tool reads don't really matter.

If possible, check the comparator with a chamber headspace gauge. After comparing the Stoney Point comparator with a 30-06 insert to chamber headspace gauges I discovered several thousandths of an inch difference. I logged the differences and take them into account when using the comparator.

Here are the readings I observed:

30-06 Headspace Gauge/ Stoney Point Measurement
Go --------2.0487”/ 2.041”
No Go – 2.0547” / 2.046”
Field ----2.0577”/ 2.049”

As others have recommended, it's a good idea to check resized brass with a cartridge headspace gauge. Until you have a cartridge headspace gauge, you can compare the headspace reading of resized brass with the headspace reading of brass on an unfired factory cartridge from a major ammunition company.

[markm]

Agreed on can over being a bad idea. If it's too much sizing, you're going to get a lot of case separation.

[Krazykarl]

Especially with tapered cases.

Missed markms quote....

[LMT/556]

Agreed on can over being a bad idea. If it's too much sizing, you're going to get a lot of case separation.

Watch for shiny rings on your brass, if observed use a feeler to locate a ridge.
I was used to sizing -.003 for a PRI which measured 1.458 fired. My new Noveske 20" measured 1.461 fired, the PRI die setup caused stretching of my Hornady brass, observed as a shiny ring about a third from the base. If you can feel them with a feeler the brass is trashed.