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

^^^^^^^
Good post! Puts things in perspective.

Been loading over 50 years and this is what I do. Numbers don't mean a thing if the cases don't fit YOUR chamber.

Why bother with weighing powder? Just put in what looks right.

I've had the stoney point headspace gauges 20 years, from back before Hornady bought them out. They've long since been amortized and it takes about a second to mount it on my calipers. Going by the "slight resistance when closing" method can fool you because there are other things than the shoulder that can cause the same feeling like an expanded case head or tight neck. Measuring something instead of guessing is never the wrong answer.

+1...... To what Crow hunter said.... Got my Stoney Point headspace gauges back around the mid 1990's IIRC. I have all the headspace data written down for each rifle. Put gauge on caliper; take measurement and instantly know what the story is. I think the folks at Hornady recognized what a great product Stoney Point had and that's why they bought 'em out. Nice part is that they didn't change anything. I can buy a Hornady bushing today and use it on my 20-something year old Stoney Point tool.

That's a pretty solid indication you don't understand what we're measuring or why. The zero measurement I showed above is on fired brass from YOUR chamber. The entire point of measuring is to know where the shoulder is set relative to YOUR chamber. It ain't hard, but without measuring you're just guessing.

All of the techniques described above to avoid measuring headspace are more tedious and less accurate than just measuring it.

The Forster Datum Dial Measurement System works very well for measuring case headspace in my experience. It clamps on a vernier caliper and measures the headspace for unfired and fired brass in the specific bullet cases offered in the set. Standard set measures from 17 Rem to 375 H&H.

https://www.forsterproducts.com/product-category/inspection-measurement/datum-dial/

It's very easy to measure fired brass for each of your rifle chambers. Then size your brass in to the spec measured by the datum dial.

Bruce

Great thread - great info. ..

So you are measuring the distance from the base to a datum on the shoulder(headspace). As I understand you, you are then setting the shoulder back some amount (.001-.002) Why? If I PFL size or necksize. I am not touching the shoulder so am working my brass less. When PFL or necksizing no longer allows chambering, I FL size just enough to once again allow chambering. What does knowing the dimension to an arbitrary datum gain me? What have I been missing all these years?

I do the same thing Blacktailer, and have been for years. The only reason I bump shoulders back is when brass gets a little too tough to chamber. My brass lasts a very long time.

I think at least part of the percieved issue here is about different applications; what works for a guy shooting 10-20 shots from a bolt action may not work for the guy shooting 500 rounds through a semi-auto, for example.

Partial full length sizing is certainly a viable option in some bolt action and single shot applications, and I've done it quite a bit myself. It does not work for everything though, and makes closing or opening the action unreliable in some guns (most semi-autos and pump actions for example, or when firing a lot of rounds in a bolt gun and the chamber gets fouled or dusty). This discussion is not about partial full length sizing though, or about neck sizing.

Measuring shoulder bump comes into play when you FL size. Instead of guessing "just enough", you can actually measure exactly enough shoulder bump to be correct for your chamber. It's less critical in a bolt action in a clean environment with plenty of camming power, as long as your "just enough" isn't too much, but in other actions or in severe environments, the ability to measure and bump the shoulder the right amount can be the difference between a gun that won't cycle or extrac, and having excessive headspace.

One example I'll point to is the commonly suggested method of adjusting a sizing die down in 1/8 turn increments until the action closes. If you actually measure (or do the math on die thread pitch), 1/8 turn is equivalent to ~.009", meaning one increment can take you from not closing the action down to excess headspace. If you're actually measuring shoulder bump, you'll catch that immediately, but without measuring it would feel fine and the owner wouldn't realize the headspace problem he created.

Agreed. Pumps and autos are a whole different animal.

Good explanation of the process here:
https://youtu.be/Qd583ZMYncE

+1

I wonder...if partial full length sizing doesn’t bump the shoulder back, wouldn’t it potentially move the shoulder forward since the side walls are being partially compressed, forcing the shoulder forward??

It does...but try it your self to see.

Run the die down to your lock ring. Just so you know where you`re at. Then turn back out 3-4 full revolutions. Start sizing the case, and move the die down 1/2 turn. Check the case in your rifles chamber after each turn. Do it again etc. See what happens.

Yes, that's exactly right. As the body diameter (at the shoulder) is squeezed inward by the die, the shoulder moves forward gradually, up to the point that the die shoulder contacts it and pushes the case shoulder back.

Results vary of course, but in a number of different cartridges I've measured .001"-.002" shoulder set forward. The maximum set forward happens right before the shoulder is set back. If you're partial full length sizing and leaving a significant part of the neck unsized (like 1/4 of the neck, maybe), the shoulder set forward happens but is very small; I've measured .000"-.001" max. In a bolt action with plenty of camming power, that is no problem at all. In something like an AR15 - it can work, the bolt will close, but it is usually very hard to open again unless you fire the round.