Help with Case Headspace Measurements

[South Pender]

I've been looking at gauges for head to shoulder measurements and two options appear to be: (a) the LE Wilson headspace gauge and (b) the Sinclair inserts in the Hornady comparator body. With the Wilson gauge, I can see that it would be easy to check max and min headspace of cases, but I'm wondering whether you can measure the reduction in headspace after resizing--where you'd presumably end up somewhere between max and min on the gauge. But I may be missing something with the Wilson gauge. The Sinclair insert/Hornady comparator body option would seem to make it easier to measure exactly how much you have bumped the shoulder after resizing.

I've never bothered with this in the past. I've just full-length resized and ensured that the cases would chamber without resistance. But I may be over-resizing my cases and would like to have a way to resize them minimally--with minimal shoulder bump, but enough to chamber easily.

What would you guys recommend? There may be better tools out there that I'm unaware of.

 

[jepp2]

What would you guys recommend?

I use the Hornady Lock N Load bushings.
https://www.midwayusa.com/product/1012743827?pid=479704
I record 3 measurements in my records:
- Length of case head to datum after the first firing (I also record the same prior to firing)
- Length of case head to datum where I can just feel the stripped bolt close on the brass
- Length I want to size to (0.001" less than where I feel contact)

It can take multiple firings before the case head to datum is long enough to feel the bolt close on the brass. To speed the process along, I set my sizing die high, which causes the shoulder to lengthen during sizing. I have seen new factory brass more than 0.010" shorter than my chamber headspace before firing and still 0.008" shorter AFTER firing. So the folks that say set the shoulder back 0.002" from the fired dimension, might be causing issues.

 

[Zero333]

Yeah... most of us use the hornady headspace comparator with appropriate bushings... get the kit.

There is also the RCBS precision headspace micrometers. But they're cartridge specific
https://www.rcbs.com/case-prep/measure/precision-mic/564.html

whereas the hornady comparator comes with 4 bushings that cover 99% of cartridges.

 

[K22]

The Wilson gauge will not give you a precise measurement since it is designed for standard SAMMI chamber tolerance. It's a useful tool for a quick qualitative check but not for measuring precise shoulder bump. It can be done with a dial gauge and stand but there is a much easier way.

The Hornady or Sinclair tool when used with a caliper measures precise shoulder set back and is relatively easy to use. Widden Gun Works also sells caliber specific bump gauges. Any one of these will do the job. I personally like the Widden gauge since it is caliber specific.

You are on the right track wanting to measure shoulder set back. It the best way from an accuracy and safety standpoint to properlyset up your full length sizing die to avoid over sizing and sizing for reliable functioning.

 

[Cap'n]

Look at the Forster Datum Dial. It's a very versatile tool, comes in a kit that will handle most calibers.

One thing to remember about the LE Wilson case gage is that it can be used to give you a measurement of your fired or sized cases vs. the max SAAMI cartridge spec. The Hornady, Sinclair, and Forster tools all measure a relative shoulder length that compares cases measured with the same tool. As K22 said, to get the physical measurement with the Wilson Case Gauge you will need Wilson's micrometer top, or a depth micrometer or dial indicator/comparator stand to get measurements vs max SAAMI from which you can calculate the amount of shoulder bump. But don't try to get the measurement using the depth rod feature of your calipers.

The case gauge and measurement tools will give you more precision that any comparator/caliper, but is overkill as all you really need is about .0005" resolution. I use the Forster Datum Dial but I like having the Wilson case gauge also, because it gives me a visual confirmation of what I am doing to the case during sizing. In a prior life I attempted to bump shoulders without having a good measurement tool and by having the FL die backed out too far I increased the CBRSL and ended up with stuck cases that would not chamber.

 

[powderbrake]

One word of caution.

Once you select an item to measure headspace, the numbers you record are for THAT DEVICE ONLY.
You cannot change from a Hornady to a Sinclair, or to a different Hornady or Sinclair insert, and get the same readings.

This is not a problem, just ALWAYS use the SAME device.

If you change devices, start over with your reference measurements.

 

[South Pender]

Thanks to all for your helpful comments. I guess I'm coming around to thinking that my best bet (and not an overly expensive one) is the Sinclair Shoulder Bump Gage Insert in the Hornady Comparator Body. So just to confirm that this will do the job for me: Will this setup allow me to get accurate measurements of shoulder bump after full-length resizing? I gather that I would begin by measuring the head-to-shoulder measurement of a fired, but not-yet resized case, and then repeat the measurement on the case once it is FL resized, with the difference between the two measurements being the amount of shoulder bump. Correct?

 

[JFrank]

Follow this link to Innovative Technology digital headspace gage

www.larrywillis.com

 

[M21]

Also look at RCBS Case Mic I believe they call it.

 

[South Pender]

Follow this link to Innovative Technology digital headspace gage
www.larrywillis.com

Also look at RCBS Case Mic I believe they call it.

Two good suggestions. Both make taking the measurement easier.

 

[gman47564]

Thanks to all for your helpful comments. I guess I'm coming around to thinking that my best bet (and not an overly expensive one) is the Sinclair Shoulder Bump Gage Insert in the Hornady Comparator Body. So just to confirm that this will do the job for me: Will this setup allow me to get accurate measurements of shoulder bump after full-length resizing? I gather that I would begin by measuring the head-to-shoulder measurement of a fired, but not-yet resized case, and then repeat the measurement on the case once it is FL resized, with the difference between the two measurements being the amount of shoulder bump. Correct?

Correct.. keep in mind as you first start to adjust your fl sizing die the case will grow.. keep screwing the die in a little at a time till you see the shoulder starting to be pushed back.. then try to push it back .001 to .002 from what the fired case measured

 

[johara1]

I've been looking at gauges for head to shoulder measurements and two options appear to be: (a) the LE Wilson headspace gauge and (b) the Sinclair inserts in the Hornady comparator body. With the Wilson gauge, I can see that it would be easy to check max and min headspace of cases, but I'm wondering whether you can measure the reduction in headspace after resizing--where you'd presumably end up somewhere between max and min on the gauge. But I may be missing something with the Wilson gauge. The Sinclair insert/Hornady comparator body option would seem to make it easier to measure exactly how much you have bumped the shoulder after resizing.

I've never bothered with this in the past. I've just full-length resized and ensured that the cases would chamber without resistance. But I may be over-resizing my cases and would like to have a way to resize them minimally--with minimal shoulder bump, but enough to chamber easily.

What would you guys recommend? There may be better tools out there that I'm unaware of.

Very simple get a stub made from your reamer from a piece of the barrel you cut off, measure a fired case and set it back what you want. direct measurement no BS. stuff.... jim

 

[Herzo]

If you have access to a lathe, it is a simple matter to machine a gage. Take an appropriate piece of mild steel say 1/2" diameter X 1" long, drill/bore a snug slip fit hole to match the neck of the fired case and chamfer an angle on 1 end of the bore to match the shoulder angle of the case. Measure the length of the gage over the fired cartridge and compare that measurement to a new or resized cartridge. Relative measurement will tell you what you need to know. I use the Redding shellholder set to adjust my resizing dimension to bump the shoulder back 0.002 to 0.003" if necessary.

 

[South Pender]

Johara1 and Herzo, I don't have the tools or materials to do this work myself.

 

[jackieschmidt]

SP, this is what Johansson and Herzo are talking about. Multitudes of accuracy minded shooters, especially those that do their own barrels, use them It is basically the shoulder, neck, and throat of your chamber reamed into a piece of barrel. You can use it to get accurate measurements of how far you are bumping the shoulder, or as a reference to where your lands are in a fresh chamber.

If you ever get another custom barrel from a gunsmith, get him to make one for you. As was said, it is simple but effective.

Until then, any of the tools mentioned in this thread will get the job done if used properly.

The main thing is do no guess, or go by “feel”. Other things can affect how easily a bolt closes on a empty case. Getting an accurate measurement as to just how much your die is moving the shoulder is paramount.

 

[Dusty Stevens]

Get a whidden click adjust die, pma adjustment ring, or one of arkco machine’s presses with the jlc insert and bump them back .001 at a time until they chamber to your liking

 

[dgeesaman]

It can take multiple firings before the case head to datum is long enough to feel the bolt close on the brass. To speed the process along, I set my sizing die high, which causes the shoulder to lengthen during sizing. I have seen new factory brass more than 0.010" shorter than my chamber headspace before firing and still 0.008" shorter AFTER firing. So the folks that say set the shoulder back 0.002" from the fired dimension, might be causing issues.

Absolutely true: set headspace .002” back from *fully* fire formed shoulder length.

I also resize initially without bumping the shoulder until I’m sure the brass is snug on just the shoulder when I close the bolt. Then I reset the die depth to push back .002”.

It doesn’t seem to matter what comparator tool I use for the purpose. Whidden, Wilson, Hornady will all give the same result, just different numbers on the calipers.

David

 

[Twicepop]

I use a depth micrometer with a Wilson case gauge for die set ups and to verify shoulder bump.

 

[johara1]

Johara1 and Herzo, I don't have the tools or materials to do this work myself.

then get the smith that chambered your barrel to make one..... jim

 

[cw308]

I use the RCBS Precision Mic for my 308 works great for case headspace and ogive settings, very accurate and simple to use. Yes it's case specific .