Home Forums Hunting & Shooting Ask The Gunwriters Measuring case head to shoulder (headspace dimension)?

Perhaps this belongs in the Reloading forum, and I will move if appropriate or I don’t get many responses here:

I’m learning new stuff here on the the ‘Fire about reloading. Considering my age, I kinda hate to admit that. On the other hand, learning new things is great. I’m learning from many, but especially mathman and Dirtfarmer. And of course Mule Deer.

I’m learning that with the highly regarded Lee collet neck sizer dies, occasionally you need to move the shoulder back. I’ve learned what a body die is and that you can make a pretty good one from the Lee full length resizing die. (I’ve also learned what a bump die is and how it is not quite the same as a body die. Different topic.) But whichever I use, I probably don’t want to move the shoulder back as much a body die is capable of. Instead, I want to move the shoulder only a few thousandths. So, I need a good measure of the head to shoulder dimension.

What method or commercial devices do you use to measure the head to shoulder dimension on cases?

I load a lot of rounds based on the 308 Winchester case. For those I use a real fancy tool, a deprimed 40 S&W case.

I put the 40 case over the case neck of the rifle brass and measure the whole thing with calipers, before and after sizing. The difference of the lengths is the amount of shoulder bump.

^^^^^^^
I've read that before, likely from you. I bet you always use the same case too, unless you are willing to reestablish your reference every time. In addition, I suppose that method works a lot of places so long as the "measuring case" rests on the shoulder of the case to be measured. After all, the datum diameter is probably just the diameter the designer picked. Nothing really special about it.

I use my Hornady LNL comparator tool. The actual measurement doesn't mean much, as long as it fits over the neck and touches the shoulder. I use the one that's meant for measuring Ogives, but I have the whole set so I end up using whichever collet goes over the neck of my intended cartridge to take the measurement.

Hornady bullet comparators will serve the purpose. For instance, you can use the .35 cal bullet comparator to get a reference measurement on the shoulder of a .30 cal case, or a .30 cal comparator insert on a .223 case.

Can't beat a Stoney Point (Hornady)

I like the Redding Instant Indicator.

It's expensive, specialized - but it can do datum line, case length and OAL measurements too - a tool that makes it easy to get a reading that's good enough - all the more because I'm using a relative measure. It's quick and easy for repeated measurements, easily zeroed with a set of go, no go and field gages and I have head space gages by thousandths for .223/5.56, .308/7.62x51 and .30-'06/7.62x63. Paying for convenience but time is money too. Makes it quick and easy, encourages checking for spring back and doing things right. Well set up the Redding is robust and maybe calipers and micrometers are more fragile. No need to have bodies and dial indicators for every cartridge and of course one tool will cover a range on both sides when the head to datum is similar like the .308 family with a range of bushings that are likely to be on hand anyway. Then too though it's well worth having anyway, one additional justification I used for adding a T7 to the collection is having the Instant Indicators and the dies all set up simultaneously. Like having a caliper set-up with the Hornady adapters for each cartridge without tying up a good caliper.

I also have some Hornady (and some from previous ownership) despite using a Starrett digital (serial port and machinist's milk tolerant but not worth the extra money for reloading bench use) I don't trust the readings to all the indicated places for actual dimensions. I also have Wilson case gages (and cartridge gages not the same thing and trimmer shell holders also not the same thing) and RCBS plastic micrometer style and Case Master dial tools.

In effect I started with L.E. Wilson gages and relative eyeball measurements and never had a complaint but I wanted a little more convenience and better numbers as time passed and the number of cartridges loaded - and the same cartridge in a break action, a gas gun and a bolt gun is sometimes not really the same cartridge - so I went what I think is deluxe.

For a tool, just about anything with an appropriately sized round hole that fits in your calipers will work. The hole size should be such that it makes contact about halfway up the shoulder. I make my own from pieces of barrel cut-offs.

Always zero on a fired case from the same rifle:


Then measure shoulder bump after sizing:

I use both the Hornady/Sinclair "comparators" and the Larry Willis "Digital Headspace gauge"...

There is no need or reason to measure, simply adjust the sizer so cases chamber with a tiny amount of resistance,.

You can sure get by using that method. Truth be told, if I move a shoulder 0.002" and still don't like the way it feels closing the bolt, I'll go another 0.001" or so...but I like being able to measure for the ease of making that adjustment. It doesn't take much movement of the lock ring the change it by too much. But you're right, it ultimately has to feel right when closing the bolt.

Exactly...if one NEEDS a measurement, stick tape on the case head, close the bolt. Measure the thickness of the tape when it feels good. About three thous, or two applications of tape.

You can do that if you want... But actual measurement before and after like I showed in the pictures above is easier, faster, and more accurate, even if you're just using an empty 9mm or 40 S&W case instead of the tool attached to the calipers. I can't see any reason to bother with tape.

Here's an article I wrote on die setup and shoulder bump last year that might help. The Sinclair Hex Bullet Comparator I used is designed for measuring OAL to the ogive, but by using a larger caliber hole than the cartridge you're loading for lets it seat down on the shoulder of the case to measure shoulder bump. Since the nut I have only has holes up to .30cal it only works on cartridges up to 6.5mm, but it's easy enough to make your own by purchasing a 1" nut (on the flats) and drilling the appropriately sized hole(s) into one of the flats to meet your needs. Sinclair also offers a second version for .17, .20, .224, .277, .308 and .338 calibers that will allow you to do up to .30 cal cartridges.

http://www.savageshooters.com/content.php?476-Sizing-Die-Setup-and-Shoulder-Bump

Yea boy! This works in spades!

https://www.midwayusa.com/product/3...-comparator-complete-set-with-14-inserts

for use on cases with no bullet

This is true, careful die manipulation, 1/16 turn at a time. When you get done, smoke a case with a candle or cigarette lighter, and carefully chamber the sized case after wiping the lube off the case.

You should see slight deformation of the black soot on half of the shoulder. If you do not see this, you have probably pushed the shoulder back too far.

Measuring is just easy, write the length down in the top of the die box or in a note book for that rifle with that particular barrel. Check more than one case as brass spring back is a real bitch to deal with as brass gets work hardened along with the fact that there maybe as much as 6% variation in hardness within a single lot# of brass.

Done that too...uses a .45 LC or 357.
It works.

I set my die up by using a fired case, sizing down till the bolt closes with no resistance. I will also check bolt close on a different make of brass, adjust if needed. YMMV.

Same here, but I opt for slight resistance when closing the bolt, or ,when I had my M14, reliable closing of the action with a full magazine. None of this small base die FLS nonsense - I wanted my cases to last! (and they did)

If you do the arithmetic, turning the die in 6 degrees---a single tick of the second hand of a clock, the shoulder should be moved further back by a little over 0.001 inch. Getting it exactly where you want it is a precise and tedious operation. That's why I leave the locking ring set once I've adjusted it.