Home Forums Reloading Big Game Rifles Properly measureing cartridge headspace

I was talking to a friend of mine who has been reloading all his life with RCBS equipment. He said he had never measured his resized brass for headspace, ever. I asked him how he set his dies and he said he did it long ago and never thought about it.

Do any of you actually use precision tools to measure the brass headspace?

Another friend of mine has an RCBS micrometer headspace guage for his 308. Looks nifty.

This article brags up some stoney point doodads, but nonetheless it has a nice cutaway photo of a rifle chamber.
http://www.realguns.com/archives/093.htm

What are you all using and doing for these measurements?

Of course, I measure how much my dies move the case shoulders every time I size a batch. The Stoney Point caliper attachments work quite well.

You can make the cartridge fit the chamber properly without knowing the measurements of either.

Bruce

True, and when the subject has come up I have outlined a procedure for doing just that. But for me measuring how much my sizing die bumps the shoulder is the way to fly.

I load for five different 308s for example, so I can't have one die with its lock ring set once and never touched the way some folks do it. Besides this isn't perfect even in the one rifle case either. I try to move the brass a very small amount and different types of brass or the same brass on different firings require slightly different amounts of die action to achieve the same dimensional change. I don't want to go through the cut and try procedure fitting the brass to the rifle every time.

After initial familiarization with a particular rifle I don't worry about its chamber dimensions as long as it isn't an outlier.

I have the RCBS Precision mics in a couple of calibers. They seem to work good for checking how far you have set the shoulder back, but I feel like there is a better system for setting the bullet where you want it. I am just about to look into some Stoney Point stuff for that.

Mathman, that is an excellent procedure on how to size.

Your gun will tell you when you have eliminated the gap between the case shoulder and the chamber shoulder when the case becomes tighter in your chamber and develops a crush fit. Most of the time this happens somewhere around the 3rd or 4th reloading. The headspace gauge allow you to follow the case expansion through these loadings, assign a specific dimension and check for a crush fit without having to chamber each case.

I use the Hornady Headspace Gauge which attaches to your caliper


and measures at or close to the datum line


This will give you a dimension that is relative to that specific chamber and case and can be recorded for future use. What it really lets you know is if your chamber and that brass has an excessive amount of HEAD CLEARANCE. Head clearance is the gap dimension between the point on the case that first hits the chamber when pushed forward by the firing pin and the point in the chamber that stops forward movement.

In a belted case this is more complicated because the front of the belt is the part of the case that stops forward movement. In an unbelted and unrimmed case the part of the case that stops forward movement is the case shoulder or datum line. What you have to realize is that on a belted case there is still a lot of gap, call it datum line clearance, at the shoulder even though the case has been stopped by the front of the belt.

For instance the following dimensions taken with the Hornady Headspace Gauge on cases that are neck sized only until a crush fit develops are typical:

30-06 Steyr factory
New case - 2.040" (subtracting the 2" the attachement adds)
Once fired - 2.0485"
Twice fired - 2.050"
3 times fired - 2.051" (slight crush fit)
4 times fired - 2.0515" (crush fit)
Now you can use a body die and the gauge to set the shoulder at 2.051" or 2.0505" for a slight crush fit

300 win mag Beretta Mato
New case - 2.253"
Once fired - 2.270"
Twice fired - 2.272" (slight crush fit)
3 times fired - 2.2725" (crush fit)
Time to set the shoulder back

On the 30-06 the measurement for the HEAD CLEARANCE is 2.051"-2.040"=.011". For the 300 win mag the HEAD CLEARANCE is 2.272"-2.253"=.019". The measurement of head clearance on the 300 win mag is not part of the headspace because the belted case headspace measurement is determined by the distance between the front of the belt and where it hits in the chamber. The measurement of head clearance on the 30-06 is a part of the headspace dimension and the headspace will vary directly with the amount of head clearance.

The HEAD CLEARANCE is as much a function of the brass as it is a function of the chamber. Brass manufacturers always seem to undersize the belted brass and this is why the belted cases are more prone to a case head separation.

I don't own any RCBS Precison Mic's but I think you have to buy one for each caliber. If you buy the combination set of collet for the Hornady Headspace Gauge you are set for whatever you reload for.

"Brags up"?
The purpose of the article wasn't intended to endorse a product or even a procedure as much as it was intended to show some basic tools, their intent and how they are used. You'll find reference to products from Wilson, RCBS, etc on the site for the same purpose.

You can set a sizer die to minmize cartridge headspace for a given rifle by using spent brass as the adjustment point of reference, however, you can't tell if a rifle is developing a problem with excessive headspace unless you find some method of measurement. Some shooters will also load to spent brass when target shooting, but load to spec when loading for hunting. Some folks load for a number of rifles of the same caliber and want to identify the minimum common cartridge headspace. We do a lot of handload development, so we log a lot of cartridge and rifle data.

The most useful tool from my purposes is the COL gauge. Sometimes chambers are cut short below minimum and loading to a manual's COL will park a bullet against the rifling. In other situations where case capacity is tight there may be room to seat bullets out a bit and gain a half grain or so of capacity. Additionally, bullet length varies with production lots so measuring at the bore diameter of a bullets ogive set COL to account for the important dimension.

Is all of this necessary? Probably not. There are alternative methods, but these tools do provide more information when making handloading decisions.

Can these be used on Weatherby Calibers?

Thanks

Hornady bought the Stoney Point doodad... correct? Its the same thing- right?

"Do any of you actually use precision tools to measure the brass headspace? .... What are you all using and doing for these measurements?"

Yes, and I use both the Stoney Point/Hornady type tools and the RCBS Precision Mics as well. Love 'em both. But, technically, it's not precision head space measurements, it's only a precise measurement of fired and then resized cases.

To use any of them, I find the length of the fired case shoulders and duplicate that when resizing, it's no more complex than that. When setting up a sizer, most folks try to set the shoulders back a couple thou more but that's NOT neccessary. A fired case shoulder is already slightly short of the chamber shoulder due to normal springback do moving it back further only increases the rate of stretching.

Is it "neccessary" to do that? Obviously not. We have been reloading brass cases since they were developed, well over a hundred years now. We only got easy to use and fairly inexpensive tools to make those meaasurements about 20 years ago. It's wise to use them, mostly for best case life, IMHO.

Long before I understood the concept of headspace--or started measuring it--I was making accurate hunting ammo. Maybe I was just lucky.

But when I started PFLR my cases, the accuracy got even better, but I still didn't know how much I was squeezing the case or pushing the shoulder back.

The Stoney Point Head & Shoulders Gauge--now known as Hornady Headspace Gauge--is one of the better handloading gadgets to come along in recent decades--in my semi-humble opinion . Along with the SP comparator (now produced by Hornady also), these two items are couple of my "must haves" on the reloading bench.

But I don't use my SP OAL guage anymore, the old fashion method I use is easier......


Casey

I use Larry Willis' headspace gauge and it works perfectly:
http://www.larrywillis.com/

When using the same die for several rifles (I own 3 x 338 WM, I set up with Sinclair shims for each rifle:
http://www.sinclairintl.com/product/6170/s

Looked at the Hornady LNL "Headspace" Gauge last night. Looked simple enough. Today spent time using/experimenting with MEC powder bushings to gauge shoulder set back. They seemed to work fine. Have most of the different bushings and was able to find what I needed to fit. And they worked well on several Weatherby calibers.

Yes. The measurements are actually relative in that they are NOT taken at a very specific point, only close to the middle of the shoulder. On a 300 Wtby I reload for I just use the collet for the win mags.

There you go!--ingenuity at work. I would just make sure the bushing is sitting flat on the caliper jaw, it would probably be easy to have the bushing cocked a little bit without realizing it (if that's how you're measuring it anyway).


Casey

Hi Casey,

That what I thought originally, but the big wide lip at the top of the bushing sets itself pretty easy. It has the same feel as using an inside mic. Actually it was pretty quick and repeatable over a couple of bushings - for the bigger calibers. e.g. - 7MM Rem Mag - Bushing numbers 27 ,28, 29 all gave the same change of 0.004" shoulder set back.

Bushing diameters - Correcting the diameter for the thickness of the caliper blade is only 0.00004" - so rounded to 3 deicmals. So these are very close to the 0.420" of the Hornady bushing used for the 7MM Mag, etc.
27 - 0.411"
28 - 0.418"
29 - 0.424"

I centered the base of the brass against the sliding jaw. Centered the bushing on the fixed jaw. Supported the bushing/brass with fingers and slowly rotated them until they centered themselves - which you could feel. Ignored the reading until had the feel and checked the numbers.

There you go.....just like said above....good ingenuity at work.
But I can positively endorse the hornady bushing tool.....I've had one for years. I'm sure the larry willis thing is good too.
And...lastly for those with multiple guns in the same cartridge I can endorse the shim kit (if sinclair still sells it) called "skips shims". It's a small bag of shims for under the sizing die that range from .002" all the way to .010"....you can use one or combos to set the die for all the guns in your case without touching the lock ring.

Would have bought the Hornady Kit last night if they had had it. They only had the individual bushings. Didn't want to wait, wanted to know what was going on. I have a lot of patience, just not for very long.

On the 7MM Mag, used some 0.002" (only size I had) shim stock and put the shoulder back 0.002". Will look into the Sinclair shim kit. Thanks.

Most shooters don't have the time or the patience to go through all the time consuming proceedures to measure their chamber clearance (at the shoulder).

That's a good reason to check out our Digital Headspace Gauge. It's designed to compare one of your fired cases to one of your resized cases in a few seconds. Then it displays the difference that is the clearance that YOUR handloads will have in YOUR praticular chamber.

There's no need to locate a datum line or to record a bunch of measurements. All you need to know is the clearance that YOUR handloads will have in YOUR chamber (at the shoulder). Knowing that makes it easy to set your die height "perfectly".

Check it out on our website

- Innovative

The numbers and measurements were to verify that the method I used was accurate and repeatable at various locations on the shoulder - which they were.

No number crunching, computing, etc. involved. No datum lines to find - just a relative place on the shoulder.

Takes 30 seconds to check. Put the fired brass and the bushing in the caliper, zero the caliper. Put a sized brass and the bushing in the caliper, read the caliper. Caliper reading is shoulder setback - in my case the caliper reads -0.002"