Question about measuring headspace

One can go too far

with making too much of bumping their cases. The bolt of specific rifles stripped is, in my opinion, the best way to determine the proper headspace for that rifle. It is the easiest thing in the world to do and doesn't require any special tooling to find the feel of a shouldet lust touching the chamber. Why make the process more complicated than it needs to be? Once one has their die set,where is the need to measure? Feel is feel. I have several chamber guagues but don't use them very often.
 
Pete

I respect your views, but checking a case shoulder clearance by feel is NOT the way to do it. At best, you are guessing.

I have personally checked shooters who were doing as you say, and some were bumping the shoulders back as much as .005 to .008.

A good friend of mine attended Tony Boyer's school a few years ago, and one of the first things Tony ask him was how he was checking his shoulder bump. The shooter said by "feel'.

It turned out he was bumping the shoulders almost .010. Tony told him that is why you don not use feel.......jackie
 
Jackie et al.

In my experience, the best way to do this for competition shooting is using a combination of methods. Shoulder gage and the stripped bolt test.

Using a shoulder gage/caliper is good method to insure a rough estimate. I use this method to rough set dies, and to keep shoulder bump dimensions at a minimum to avoid the problem you addressed.

This can also identify if a FL die is doing its job, by sizing the case sufficiently to keep the body from restricting the chambering of the brass.

But, I’ve found that most individuals are unable to measure truly to .001” or less with this setup.
They inadvertently move the shoulder back greater than .001”, thereby reducing the life of the case, and causing the dreaded extraction problems that so many shooters contend with.

I’ve found that by sizing with minimal shoulder setback to achieve the light press fit of the brass in the chamber over a stripped bolt, the amount varies between .0004” and .0007” of setback.

I made a special gauge to to measure this (see attached photo)

This special gauge isn’t necessary for the BR shooter, although would be handy for the shooter that uses a spring-loaded plunger ejector, since the light press-fit feel is difficult to sense with this type of bolt.

This isn’t a sales pitch for the special gauge, because it’s a mean little job making them right…but it is a sales pitch for our static-ejector setup that doesn’t have a spring-plunger applying pressure to the back of the case. :D

Greg Walley
Kelbly's Inc.
 

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This is a great example showing how shooters are often confused about determining their chamber clearance. Jackie has it 100% correct. There are many old inaccurate techniques that should be abandoned. Forget about using the "feel" method by removing the ejector. Forget about using soot from candles and/or magic marker stripes. Forget about raising your die by 1/8" of a turn. Those methods were barely acceptable back when cartridges were first developed.

Gary's gadget is an inexpensive and functional option. Our Digital Headspace Gauge uses the same principle of comparing your handloads to a fireformed case. This is 2009, and there's no need to disassemble your rifle to make precision handloads. Read the homepage of my website, www.larrywillis.com and you'll see how simple this procedure can be.

- Innovative
 
Jackie

I agree that when the round goes off, the cartridge fills the chamber. What I'm probably thinking too hard about :) and I feel is a questionable area of concern, is when the cartridge ignites...the bullet is going to move before the case fully expands to the chamber, just that "path of least resistance" rule.

So, say someone has a chamber with a headspace of 1.63" (roughly what mine is) and not knowing how to exactly measure the headspace and ends up with a cartridge of say 1.62 and loading a bullet .010 from the lands, is it a safe bet that the cartridge will when fired move back against the boltface compressing the ejector spring giving the bullet now a .020 jump?

Maybe the bullet will enter the rifling before the case moves, or maybe the bullet will begin to move forward at the same time the case moves rearward possibly canting the entry to the rifling.

As soon as enough pressure builds the case will be touching every area of the chamber but I bet that little boolit is gonna pop out of the neck before the brass starts molding itself around the chamber.

So i have been trying to find a way to measure the headspace in my Rem 700 and from what I have seen, a go no-go gauge is about all that would work since the bolt wont close when it's too long, or is this a OAL gauge and not a headspace measuring tool?

Hope that reads better than my last post :D

Let me know all my theories hold water.

Wanted to add.......

With the bullet set and the cartridge against the shoulder, the jump is the same everytime. However if there is some gap in there I believe the cartridge will move back before the case fully expands therefore opening the jump.

That is where i'm kinda stuck at.
 
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Hope that reads better than my last post
Click to expand...
No

Let me know all my theories hold water.
Click to expand...
Not as far as I'm concerned.

Look. Another term for "headspace" is "head clearance." It is the distance from the boltface to the rear of the case, when the case is in it's "frontmost" position in the chamber. In benchrest, that should be about .001. As far as case sizing setups go, we'd all be better off using the term "head clearance". Reserve the term "headspace" and the measurement of those gauges used to cut a chamber. But remember, when you cut a chamber, you are still fixing the "head clearance."

The whole point of go and nogo gauges has to do with factory brass and SAAMI specifications. Not an issue with benchrest. To illustrate this -- Question: why do you need a go-gauge for a wildcat? Answer: so you don't have to make a new sizing die when you fit a new barrel.
 
Given Jackie's observation that adjustment of the dies by the "feel" method has given some people a head clearance of .008 or more, I just though of a way to test the "feel" method. Strip the bolt, adjust the sizing die by "feel."

Now, put a piece of scotch tape on the back of the case. (If you could find a way to use plastigauge, you'd have a better test.) If the bolt will close with the tape on the back of the case, esp. without scarring the tape, say what Alan Greenspan said: OOOOOPS!
 
There are a jillion ways to get your handloads closer than just "bumping the shellholder". However, nothing beats taking an accurate measurement.

- Innovative
 
Headspace is nothing but a standard. It is used to insure that a rifle
made by Remchester in USA has the same chamber as a CZ made
where ever. This allows ammo to be made nearly anywhere, and it will
be safe. This headspace thing allows reamer grinders , ammo makers,
gunsmiths and all to be on the same page. This is of course , has
tollerances. Lets call the bolt face point zero. FRom there we go
forward to a point on the shoulder. Not the whole shoulder, but a point
where the shoulder has a certain diameter. This is called a datum line.
Not all dies, and reamers will be exactly perfect. So this allows us
to qualify what we are talking about, without the maybe its a bit
this or that.
The bump gauge as made using the same reamer, does this nicely
because it should be a perfect match. The Larry Willis thing will
do the same, by meeting the shoulder at a constant point in diameter.
Thus it becomes a datum line.
The Fly in the soup, is as previously mentioned that if a case
is measured before it has been fully formed, it will not give you a
true measurement. A case will not be fully formed with starter
loads, and often not with normal loads the first time. Neck sizing
untill the case is formed would be better. However it is sized, there
should be no shoulder set back( we call it bump). Another Fly in the
soup is the primer. If it protrude in any way, you will get false readings.
Using rods down the barrel , or behind bullets is poor, as
measurements cannot be made accurately.
A case fired at normal pressure 3 times, will not be opposed
or kept away from the boltface unless you are setting shoulders back.
If your gun came to you without a shoulder bump guage, you
can still make one. A piece of steel, with a hole thru it approximating
a diameter which will meet the shoulder half way on the angle
can be used. It should of course not have sharp edges and should
be square on both ends. As with the bump guage, this is a relative
dimension, meaning that what ever number you get does not
relate to anything other than your measurement, and your guage.
It has no relationship with anyone elses numbers.
True wildcats, often have no headspace standards. The
creators , fully understand the way a case needs to fit a chamber.
and operate accordingly. As a precision shooter-reloader, it is
your chamber that dictates all your loading. Once the gun is made
and chambered correctly, headspace becomes a non issue and
all loading has one purpose. That is to match your chamber, safely
 
Once the gun is made
and chambered correctly, headspace becomes a non issue and
all loading has one purpose. That is to match your chamber, safely
Click to expand...

Bob,
Your description of headspace (above) is partly correct. However, if your goal to get the maximum accuracy and the maximum case life - you can do better if your chamber clearance is as small as possible.

- Innovative
 
I too like Bob's response, but there are short range benchrest assumptions built in there. Of course, this is Benchrest Central, so fair enough.

Essentially, SAAMI (or CIP in Europe) headspace numbers specify how far a factory round (virgin case) should go into a factory chamber to be safe to fire. If it is a rimmed or belted case, the chamber distance to the case shoulder (if it has one) is not specified.

And the datum line is again for chambering, not resizing. With my 40-degree shoulder chamberings, you can see that where the FL resize die is moving the brass is on the body-shoulder junction, and it does take the body down just a touch at that junction.

The point is, there are several things that can prevent a case from easily going farther into the chamber. As far as that goes, there are several relationships that determine how both the barrel and the case expand and contract during firing, as both do. Just chamber up a barrel with a 1-inch tenon with a .540 diameter case. That tenon is thin enough that it expands enough so that when it snaps back, it can grab the case if the case has only .001 or .002 clearance. But that's not a benchrest situation.

None of this is to suggest that people skip measuring the amount the shoulder is set back with the proper tools. But first, be sure that what is impeding case movement is the shoulder, not something else.

And if it is partly the shoulder, and you measure, and size it back, but a case still doesn't fit well -- is hard to chamber -- figure out why. Further sizing the shoulder back perforce sizes the base more if there is any taper to the case, but is the wrong thing to do. If you are new to the sport, or aren't well versed in all the things that could be happening, take it to a gunsmith -- a skilled gunsmith.
 
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Larry Willis

Larry,
Given that this fellow, has little to no understanding of Headspace
and its relationship to his ammo, or how to make what he has
work safely . I think what I have said is on target. He , having the gun in hand, has no further control of what his chamber is or how tight it
is. Some of the factory offerings in PPC have very large chamber and can
still be made to shoot, when one understands what he has and where he needs to go. Simply going to your local hardware//sporting goods and
picking up a set of dies marked PPC doesn't cut it. Nor does screwing dies
down on shell holder, without knowing what he is doing.
I offered this explanation in the most basic way, because he did not
seem to follow what Jackie and Greg Walley, Gary Walters
and others said. This is not Rocket science, but some understanding
is needed.
Your guage is nice and well thought out I'm sure, but I have enough
fragile things on my loading table. I can even operate it with out knowing what I'm doing, The only thing that can happen to a solid bump gauge
is I might lose it
 
Charles E

Charles E,
You are of course correct, many things can impede a case
in a chamber. Datum lines are not for sole use in grinding reamers.
when measuring anything with an angle on an end it can be used.
It becomes relative to you and your cartridge case, and your chamber,
and of course to your measuring devise. If your setup/ devise says
that with a fully formed case the number comes to 2.000 inches,
bumping the shoulder to 1.999-1.9995 should work. Some
knowledge of measuring is also needed. We that work with
measurements easily forget that the guy who files legal briefs
should grasp this , its not so.
When you are using a bump guage, you are creating your own
datum line, its a reference only.
 
Bob,
I agree that when you use a custom resizing die that's made for your particular chamber, there's no need think about headspace. Our Digital Headspace Gauge and other basic tools (made for measuring chamber clearance) are helpful when production resizing dies are used. The acceptable headspace tolerance then can be tightened by setting die height perfectly to operate like your custom benchrest dies.

- Innovative
 
@Larry Willis, let's allow that you make good products, as indeed you do. But please limit the plug for them to one or two per thread.

@Bob, what I was trying to suggest is that for resizing, a gauge which hits only on the datum line, and not the full neck/shoulder -- shoulder -- shoulder/body junction would not work for my 40-degree chamberings (and there is more than one which behaves this way), as what seems to always get sized is the shoulder/body junction. I've never had a chambering where the point that needed the "bump-sizing" was the neck/shoulder junction, but I wouldn't rule it out with a long, gentle shoulder a la the 25/06.

A gauge made from the chambering reamer that covers all these points would of course work fine.
 
Charles,

I'll be careful to limit any unpaid advertising here. However, as you can see there are a LOT of shooters out there that are still using tape, soot from candles, magic markers, and vodoo or all sorts to adjust their headspace. Production dies and production chambers are made within a wide range of so called "acceptable" tolerances.

I'd just like to advise shooters who don't use custom resizing dies, that the clearance of THEIR handloads in THEIR particular chamber can (and should) actually be measured. I've used Gary's gizmo method for years, and it works. (no plug for Gary's gizmo is intended ....)

- Innovative
 
Bob Kingsbury said:
Larry,
Given that this fellow, has little to no understanding of Headspace
and its relationship to his ammo, or how to make what he has
work safely . I think what I have said is on target. He , having the gun in hand, has no further control of what his chamber is or how tight it
is. Some of the factory offerings in PPC have very large chamber and can
still be made to shoot, when one understands what he has and where he needs to go. Simply going to your local hardware//sporting goods and
picking up a set of dies marked PPC doesn't cut it. Nor does screwing dies
down on shell holder, without knowing what he is doing.
I offered this explanation in the most basic way, because he did not
seem to follow what Jackie and Greg Walley, Gary Walters
and others said. This is not Rocket science, but some understanding
is needed.
Your guage is nice and well thought out I'm sure, but I have enough
fragile things on my loading table. I can even operate it with out knowing what I'm doing, The only thing that can happen to a solid bump gauge
is I might lose it
Click to expand...


Who's the fellow? Who's not safe?? That's quite a stern accusation IMO.

I will say that all the above makes perfect sense and I understand what headspace is, very much so.

I understand that when the case is formed it will be pretty much close to the size of the chamber after the springback.

My rifle is not a factory chamber, generally all I do is necksize and if there is a problem closing the bolt, I will bump the shoulder slightly.

I was simply throwing out a scenario, that if a shooter was to try to measure the headspace in their given rifle, how does a digital gauge or one offered by Hornady, replicate the chamber of your rifle?

Sure I can measure the distance from the base to the datum of the case, is this the exact same datum that is in my chamber?

The piece Gary showed of the barrel stub which would I assume be cut from the same reamer would be a good tool.

Maybe your actions dont have a strong ejector spring like mine, I have seen gauges that go into the chamber that when you close the bolt, the plunger compresses in the neck and you measure that way. But what if the ejector spring is stronger than the plunger spring and the base of the case is held off the bolt face? That's my question.

No, it's not rocket science, but tell me how you measure the distance from the closed boltface to the datum on the chamber where the shoulder is measured, when the bolt is closed.

Are we taking a fired case and guessing springback?

When I close my bolt, is the base of the case against the boltface, or just a few thou off?

Yes i'm striving for accuracy, and I like to know what makes what work.

What I have done is take a cartridge that is hard to close the bolt, measure the headspace, and use that as a max size. Knock that case back .001 and the bolt closes much easier.

I have no problem measuring my chamber headspace, took a few cases to determine max length but for the OTHER shooters that would like to drop in a gauge and read the max distance, how or what would be the easiest way.

1.629" is where I feel alot of resistance, I size to 1.627" and all is good.

The part about the bullet jump is part of "what if the case is pushed forward in the chamber by the spring...would it make much or any difference when you cook it off?

Wasn't trying to demolish the OP's thread, just had a few ???'s.
 
The part about the bullet jump is part of "what if the case is pushed forward in the chamber by the spring...would it make much or any difference when you cook it off?
Click to expand...

1. Since we are aiming for a case head clearance of .001 (I assume what you're calling "headspace"), the answer is no. One thousandth more or less of bullet advance will not affect accuracy. If it did, we'd just set our bullets with .001 less jam or jump. Personally, I don't even test bullet jam in .001 increments. The barrel would be gone with testing, and I'd be forever chasing the throat erosion.
 
gtofan ......

Many good shooters are still neck sizing, and they occasionaly bump the shoulder back. However, most of the top shooters in benchrest are FL resizing, and hunters should always FL resize. Here's just one very good reason why.

Most rifle cases are tapered. That means when you use a FL die, it also reduces the case "width". The next time you FL resize a case, notice how much more pressure it takes. The real force is applied to the lower part of the case, not on the shoulder. (If you ever get a "stuck case" this is where it will grab.) You can push a case shoulder back by .010" using a modern press without even feeling it. It's best to also resize the case wall (tapered part of the case), but find out exactly what you're doing to your case shoulder.

- Innovative
 
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