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Old June 11, 2011, 04:14 PM   #1
Brian Pfleuger
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About This Thing Called Head Space...

So, I've got the fancy Hornady headspace gauge tool.... nifty gadget it is.... and it raises more questions that it answers...

I'm measuring fired, unsized, Norma 7mm-08 cases from my Encore. I find significant variance. A large population, about 50%, are where I zero the calipers. I have cases that measure as much as .010 shorter and as much as .007 longer than the "reference" length. Confusing, this is, since I am trying to set up my Redding body die to bump the shoulder by only .001-.002. Longer, I can deal with, shorter, well that's an interesting result in itself. See, I set up the die to bump the shoulder .001 off the "reference" length. All is well, except, oddly, when I run the shorter cases through.... they get shorter yet. That, I don't understand.

So, I go to fired, unsized Norma .204 cases. Same thing. Several different lengths, with a max/min difference of around .012. I measure them against loaded ammo that has been neck sized only, in a Lee collet sizer. Same number distribution, roughly.

Question #1:

How come cases from the same box, fired in the same gun, sized the same way, have different shoulder measurements?

#2
If I only run the cases into the body die and don't run them all the way to the shoulder, the shoulder measurement gets longer. This I understand, the brass has to go somewhere, but how come when I run the SHORTEST case in there, with the die adjusted to subtract .001 from the "reference" length, the short case gets SHORTER? That, I don't get. I would have expected the measurement to grow, by about .003, because that's what happened when I was adjusting the die and not yet bumping the shoulder...


This headspacing thing, that I thought this fancy tool would help me with, just got complicated.
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Old June 12, 2011, 12:13 PM   #2
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Pictures?

take 10 cases of extreme +/- and 10 "norm" and run them all through the die and report the results
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Old June 12, 2011, 12:52 PM   #3
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Quote:
Originally Posted by flashhole
Pictures?

take 10 cases of extreme +/- and 10 "norm" and run them all through the die and report the results
There aren't that many.

I'm a low volume shooter. I only have about 60 cases total and probably 20 are loaded up. Of the cases I've measured, it was about 10 "normal" and one or two at several various +/- locations.

Pictures won't help... They all "look" the same.
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Old June 12, 2011, 02:18 PM   #4
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Some of the things you have stated don't make scense? Are you measuring fired cases, full length reloaded cases, neck sized only cases or new unfired cases?

If these are unfired new cases then yes, the headspace measurements can vary. That is why we recommend resizing new brass.

If these are unfired reloads assuming they are the same brand case and you are sizing them all with the same die settings then they should measure about the same.

If these are fired cases from the same gun then they should meaure about the same. Some TC rifles have a gap between the barrel and the receiver. If you are shooting light reloads the case may not expand to fill that gap. Therefore there may be some variations is the headspace length.

1. Light loads where the case does not expand to fill that barrel gap.
2. Too much lube, dirt in the shellholder, no lube in the neck all can have an effect on the shoulders.
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Old June 12, 2011, 02:25 PM   #5
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Is the body of the shorter cases absorbing the force and compressing further? Or, balloning causing the discrepency? Is there a trimming stage on the press?

I'm not a reloader, and just trying to offer an out-of-the-box view.
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Old June 12, 2011, 03:46 PM   #6
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These are all fired, multiple times, never resized except in a Lee collet neck die. All were initially fired using light Trail Boss loads to form the cases to the gun(s). All have been fired multiple times with full or near full powered loads.

They have not been trimmed as they have never need it. The measurements are not case length, they are to the datum on the shoulder.
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Old June 12, 2011, 04:06 PM   #7
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Double-check for measuring errors. Try rotating the cases 1/3 turn and measuring again. If the lock up has any flex, the face of the caseheads might not be 90° to the case body axis. Same can be caused by a chamber not coaxial with the bore. Not entirely uncommon, unfortunately, though my own Encore chambers look pretty true.

Watch how the case head meets the moving caliper jaw. The offset in the insert adapter in that gauge is necessary for using it with their Overall Length Gauge, but can trick the user into angling the case head against the moving jaw of the caliper.

Try backing the body die out a little and running the short cases in. Do they grow longer now? If so, you just need a different setting with them to get the shoulder where you want it.

When a primer fires it can drive a case forward enough to change its headspace a bit, but I don't recall getting as much difference as you're seeing, which is why I wondered if the caliper technique might be a factor. I see two thousandths difference pretty routinely.

Try skipping the body die and just use the collet die a couple or three load cycles. Do the cases get closer in shape? Unless something is producing of off-90° effect I mentioned already, that should tighten them all near the upper limit.
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Old June 12, 2011, 04:32 PM   #8
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Quote:
Originally Posted by PA-Joe
Some of the things you have stated don't make scense?
I know, that's why I'm here asking.


Quote:
Originally Posted by UncleNick
Watch how the case head meets the moving caliper jaw. The offset in the insert adapter in that gauge is necessary for using it with their Overall Length Gauge, but can trick the user into angling the case head against the moving jaw of the caliper.
One of the things I did think of was making sure the cases were measured exactly the same each time. I noticed that the gauge body is cut off-set so that it can be centered on the caliper jaw when the set screw is tightened.

I measured each of the cases being careful to have the edge of the rim on the upper edge of the jaw for consistency and also centering the jaw on the flash hole. I also made sure to measure the cases so that they were consistently rotated exactly the same.

Now, they were not all fired in the same orientation, so that could, I suppose, have something to do with it but wouldn't that require the off-center chamber you mentioned?

Unfortunately, I didn't think to see if the shortest cases grew if I adjusted the die higher. I noticed the effect when I was adjusting the die using the "nominal" cases. The shoulder position grew by .003 until the die actually contacted the shoulder, at which point I adjusted it to subtract (as close as possible to) .0015 from the initial reading. I had assumed that the shorter cases would simply never reach the shoulder area of the die and I would simply be adding that .003 to their number. I was quite surprised when they shrank even further.

I'll have to experiment farther with the .204 cases... I sized all the 7mm cases already as they had been fired 2 or 3 times and were getting tight.
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Old June 12, 2011, 04:37 PM   #9
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The shorter cases may also have been narrower and thus squeezed forward less. If you were doing load development with these, the difference in pressure might be responsible.

How are you determining reference on the caliper? Do you have a headspace Go gauge?
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Old June 12, 2011, 04:46 PM   #10
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The cases may have been used at different load levels, that's possible. I have never bothered to segregate based on usage as I figured that with so few cases the usage would "even out" after a few rotations. The previous loads would range from as little as one starting level H380 firing to as many as 2 or 3 full power loads and a couple that experienced clearly over-pressure IMR 3031 loads.


By reference on the caliper, do you mean placement of the case on the jaw? The caliper jaw has a little cut-out that I'm lining the rim up to, like this:
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Old June 12, 2011, 09:29 PM   #11
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Got that same funny guage. I was also fooling around with measurments on the 204. Found that you can't use mixed brass for getting measurments. I took winchester fired brass and checked 10 brass and most were 1.560. Set the RCBS die up to set the shoulder back to 1.559. Checked brass that I resized before by doing to rcbs die instructions and the headspace was set back farther. Will be interesting to shoot these rounds and see if there is any different in groups. Was getting 3/4 in groups before with old eyes so shouldn't be any worse.
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Old June 13, 2011, 07:06 AM   #12
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As stated it could be the result of using mixed brass.
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Old June 13, 2011, 08:00 AM   #13
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The brass is all Norma. The only way it could be "mixed" is that it's from two different boxes that could be different lot numbers.
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Old June 13, 2011, 12:10 PM   #14
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Ok, I checked several cases by rotating them in the gauge to see if there was any variance. There is virtually none. One case showed .001, all others had zero change through 360dg.
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Old June 13, 2011, 01:20 PM   #15
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What type of firearm are you using? Is it a TC type break open type action or a semi? Bolt actions will give much more consistance readings. Some BO actions have a gap between the barrel and the receiver. Using less than fully loaded rounds may not expand the case all of hte way. Semis will not expand the case all of the way either which might account for the deltas.
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Old June 13, 2011, 02:28 PM   #16
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VEry interesting and handy for future reference. I have no doubts that you are measuring correctly since you are experienced in those kinds of matters.

When I first broke down and finally bought the fancy Hornady gauge, I also had a few surprises that ran counter to my intuition. Notably, I noticed that when using FL sizing dies to simply re-size the neck without trying to bump the shoulder back, the shoulder datum actually grew.

But that's not your case I realize. When I measure the head space on the shoulder I get variations of only 0.001" or so. And that is with different brands of brass. The only thing I can even guess about that is different from your situation to mine is that I currently have been either FL sizing or partial full length sizing (properly now) after every firing and loading. I wonder if the effect you are seeing is a result of variable loads and variable numbers of firings and only doing neck-sizing each time.

Yeah, theoretically, when you fire a round in your chamber, the brass expands to completely fill the chamber. And then it shrinks back a tiny bit each time. But I am wondering if after 3 firings, does it necessarily shrink back exactly the same amount as after 1 firing? Or after 7 firings? I know brass does become brittle after awhile, so the spring-back will not be as much. And it stands to reason that hotter loads will have a different effect than mild loads.

You say you went ahead and FL sized the 7mm cases? Presumably, they all measured the same after that? It will be interesting to see if they all measure the same after firing this time.
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Old June 13, 2011, 02:50 PM   #17
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Quote:
Originally Posted by PA-Joe
What type of firearm are you using? Is it a TC type break open type action or a semi? Bolt actions will give much more consistance readings. Some BO actions have a gap between the barrel and the receiver. Using less than fully loaded rounds may not expand the case all of hte way. Semis will not expand the case all of the way either which might account for the deltas.
The 7mm is an Encore Pro Hunter, the .204 is a Ruger M77 MkII.

Quote:
Originally Posted by Doodlebugger45
You say you went ahead and FL sized the 7mm cases? Presumably, they all measured the same after that? It will be interesting to see if they all measure the same after firing this time.
I did run them all through the body die, yes. Now all the cases that were at or longer than the "nominal" length are -.001. The cases that were shorter are still shorter. "more" shorter, actually, which is all in all the most confusing part. I suppose that the brass may have pushed down toward the head rather than up to lengthen the body.

I verified my technique with the calipers by measuring several cases and then randomly remeasuring them. I got the exact same measurements each time.
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Old June 13, 2011, 09:57 PM   #18
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Interesting problem. I don't recall what press you're using. How rigid is it? Do you have your lock rings good and snug? The reason Redding makes those competition shell holders in different thickness is to give a hard stop for the die, so you can apply some excess pressure to be sure you force the same fit each time. That way a case that goes into the die harder than another doesn't change the sizing length by causing a different amount of press stretch or thread compression than another.
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Old June 13, 2011, 10:28 PM   #19
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I'm using a Lee classic turret. The die lock ring is tightened and the press has stop "pegs" that provide a very positive stop.

A little more info, I just measured all the remaining fired .204 cases and got similar results as above, I zeroed the caliper at the measurement with the most cases and got this distribution:



They are, -.002, "nominal", +.002, +.004, +.005 and +.007.

I then remembered that I have 15 loaded, unfired cases from the same 2 lots. I measured those and they all but one measure -.003 from the "nominal", the one is -.002.
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Old June 14, 2011, 08:56 AM   #20
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Still might get better rigidity if you built up some shims to fill the gap between the bottom of the die and the shell holder. Shim washers would work in lieu of the Redding shell holders, but first you'd have to locate some the right size.

Still seems odd to get that much difference; a 0.009" span. Hmmm. From PA-Joe's point, is there any chance lube is squirting up the sides and into the shoulder area between the case and the die? As an experiment, you could try Q-tipping the lube out of the die shoulder area just before each sizing.

Another thought is to try my trick for hard-to-resize cases of letting the case sit in the size five seconds with the ram up, withdrawing, rotating 180° and doing it again. The idea is to give the brass a little time to stress-relieve inside the die. Chances are they will all come out a little shorter, but shorter and the same is better than different lengths because you can adjust the die to compensate on the next round.

You could also try annealing necks and shoulders, but it is so easy not to get that exactly the same on each case that it may help or it may worsen the situation. If you choose to try, I would use one of the slower, more controlled temperature methods (e.g., hold in fingers and rotate neck and shoulder back and forth in a candle flame until it gets too hot to hang onto, then drop into water or onto a damp rag with a twist; rub soot off later with steel wool or tumble).
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Old June 14, 2011, 09:50 AM   #21
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Thanks for the ideas, everyone.


Just to clarify, these size discrepancies are BEFORE sizing in the body die. After sizing, all the long cases and all the "nominal" cases come out at .001-.002 less than nominal.

I haven't actually sized any of the .204 cases yet to see where I end up, as I can't decide which length is "correct"....

That's the big question... where should I be adjusting the die for proper head space? Is the "nominal" correct? If I put the +.004/+.005 cases together, there are just as many of those lengths as the "nominal" length, so is that length correct? Judging from the behavior of a very few loaded rounds, I wonder if that +.005 number is closer to chamber size. I have had a few, just a very few, that were slightly hard to chamber. Those may be the few +.006/7 cases that I've found?

I agree that getting taller shell holders would be helpful. It would at least eliminate a variable.

On the lube idea, I thought of that and I have a bore mop that I use to clean out the die every few cases. It also seems odd to me that only the cases that are shorter exhibit this behavior.

I use the "5 second rule" when I use the collet die and the same idea had occurred to me for the body die. I tried it, but I am embarrassed to admit that I didn't measure for any effect. I was running under the "can't hurt" theory at the time.

Annealing.... the thought has occurred to me before, when I notice a slight difference in sizing effort with the collet die. I want to do it, but it seems like a black art to me. Maybe helpful, maybe not, maybe dangerous with the wrong tools. I remember you (Nick) referring to the candle method before. That seems like a decent thing I might try. I have a high-temp wireless thermometer I wonder if I could incorporate somehow. It has a long probe that could be held against the case maybe? Or maybe stuck in the flashhole (can't remember if it's small enough) and held up near the neck?
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Old June 14, 2011, 10:33 AM   #22
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It would be hard to get consistent thermometer readings, but the Tempilaq temperature indicator will work for you if you want an indicator.

I got your sizing and post-chamber dimensions twisted around in my mind between reading your OP and the more recent posts. I'd suggest you take your longest and shortest cases and shoot and neck size them only for several rounds; no body die. Measure after each firing and watch for each to stop growing the case headspace measurement and to start getting snug going into the chamber. You could plot a graph, and I'd bet you'll find they both converge on stopping at the same length. That growth stopping point should reflect the actual chamber size pretty closely.

Work the bolt slowly. Hatcher noted he could size a .30-06 something like six or nine thousandths (I forget which) just by working the 1917 bolt fast. Same for extraction on opening the bolt. Slow and gentle to keep from affecting the fired case size.
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Old June 14, 2011, 10:49 AM   #23
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I would reload a few at the +.005 and see how they chamber.
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Old June 14, 2011, 11:22 AM   #24
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First, why are you concerned with headspace problems in a solid closed breech handgun? I've been shooting a Contender for a long time with never a problem. If your hinge pin is worn or loose, that's about the only variable you've got with these guns besides the ultra-rare bad chamber. I see a few problems here that I've never had to deal with, but let's start with your measuring device.

Any standard set of calipers are only accurate to as little as .001" whether they are the dial type or digital, .002" may be closer for the "economy models". Some of the finer industrial mfg's do make some that read to .0005", but that doesn't mean you can manually hold and measure anything to that tolerance without fixturing.

Next, if you are using those digital calipers in the pics, the magnetic scale that is read by the LCD is zeroed nearest to the fixed jaw and increases incrementally towards the far end as you open them, supposedly to at least the length specified by the mfg. when you ordered them (four, six, twelve inches, whatever). If you are running the jaws open to your reference length, then rezeroing and measuring back to a sample case length, this method is providing huge margins for error. The scale should be more accurate within a higher number range, or by measuring your entire case length each time and comparing numbers.

The case mouths may not even be round after firing, and certainly not concentric with the case walls due to brass flow characteristics. As you previously stated, the OL and TTL both have tolerances of as much as .010" or more. Add all this up and factor in a little loosey goosey here and there....well, you get my drift. I'd set my die close to start, rotate my case three or four times while sizing, then recheck and record that number. Mark the threads across the lock ring of your die now. Turn the die in or out 1 complete revolution till your marks line up again and remeasure and record again. Use this reference each and every time you adjust, as well as rotating each case and reseating 3 or 4 strokes each. I'll bet your calipers read really closely if you're adjusted correctly. -7-
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Old June 14, 2011, 12:08 PM   #25
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I'm concerned about headspace because I want to prolong case life and get maximum accuracy:

http://www.bellmtcs.com/store/index.php?cid=172&

Besides, only one of these guns is an Encore.

As to accuracy of the measurements, the absolute number might not be right but you can't claim that the differences between cases are a result of instrument error. I get the EXACT SAME number every time I measure any given case. .012 variance is VISIBLY different. The numbers are reasonably close.

As to the case mouths being "out of round", I'm not measuring at the mouth but at the datum point on the neck and I can rotate a case in the calipers 360dg and the number doesn't change.
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