shoulder measurement on fired cases
- Thread starter rebs
- Start date
If some of your brass was made by different manufacturers, some fired more than the others, or have different annealing histories (or even different temperatures), you might experience different headspacing measurements.
Sometimes, you may see different measurement results from the same brand and age of brass, but simply from different lots. That is why most competitive shooters will start off with a group of brass of the same brand and lot number, try to rotate the brass to keep firings the same for each case, and retire the whole group of brass at some point. And, of course, they ALWAYS avoid using brass pickups of unknown history.
Sometimes, you may see different measurement results from the same brand and age of brass, but simply from different lots. That is why most competitive shooters will start off with a group of brass of the same brand and lot number, try to rotate the brass to keep firings the same for each case, and retire the whole group of brass at some point. And, of course, they ALWAYS avoid using brass pickups of unknown history.
.005 variation is huge, particularly for brass that's been fire formed. That indicates to me something is going on with the die and/or the press setup. Often, it's from an expander ball that's not set up properly in the sizing die and lubing might be a factor along with that.
rebs, can you clarify whether you are asking about fired cases or about sized cases? Additionally, were they reloaded with less than full power loads?
I have never found that an expander ball can affect the headspace of the resized case, unless it is collapsing the neck first! But, I seldom use an expander ball anyway - they are AWFUL! And, I agree that uneven lube can affect the sized case...
While I would certainly not say that 0.005" is insignificant, it is barely thicker than an average piece of copy paper, and varying cases and states of annealing can EASILY result in that much difference. I maintain my BR rifle's cases to 0.001" of shoulder set-back while F/L sizing in a custom die that matches my chamber, but only with new-ish Lapua cases, and with EVERYTHING tightly controlled. Shoulder angle also plays a part in consistency.
The "springback" of the case's shoulder is hard to control, unless all cases are IDENTICAL to start with, are at the same point of hardness (or softness if you prefer - which changes slightly every time the case is "worked" by sizing and firing), and are sized IDENTICALLY, and loaded with IDENTICAL (or nearly so) bullets and powder charges! That is my point.
Since the OP is NOT "camming over" while sizing, any slop in the linkage of the press may add to variations in headspace measuring. "Camming over" helps to eliminate that effect of linkage tolerances on the sized case.
It would be interesting to know if his fired cases show much (or any) variation. If so, the sizing process only adds to that variation. If not, the sizing process has to be the culprit.
Don't forget to deprime and clean your fired cases before you measure their headspace!
While I would certainly not say that 0.005" is insignificant, it is barely thicker than an average piece of copy paper, and varying cases and states of annealing can EASILY result in that much difference. I maintain my BR rifle's cases to 0.001" of shoulder set-back while F/L sizing in a custom die that matches my chamber, but only with new-ish Lapua cases, and with EVERYTHING tightly controlled. Shoulder angle also plays a part in consistency.
The "springback" of the case's shoulder is hard to control, unless all cases are IDENTICAL to start with, are at the same point of hardness (or softness if you prefer - which changes slightly every time the case is "worked" by sizing and firing), and are sized IDENTICALLY, and loaded with IDENTICAL (or nearly so) bullets and powder charges! That is my point.
Since the OP is NOT "camming over" while sizing, any slop in the linkage of the press may add to variations in headspace measuring. "Camming over" helps to eliminate that effect of linkage tolerances on the sized case.
It would be interesting to know if his fired cases show much (or any) variation. If so, the sizing process only adds to that variation. If not, the sizing process has to be the culprit.
Don't forget to deprime and clean your fired cases before you measure their headspace!
Rebs typo-- .0005?
Sounds like you need to lower the die down until the measurement from the base to shoulder datum changes.
I find dwell time to be important each time the press handle is lowered whether sizing brass or seating bullets.
jepp2
Gold $$ Contributor
What are you using to measure? Any feel for how accurate you are with this method? (If you measure the same case say 10 times, what would the readings be?)
That depends on your press, your die, your shellholder, and your rifle headspace.
Excellently said!
Does the OP mean .005 or .0005, if the latter, it's irrelevant. If it's the former, see Mr. Ken6PPC post.
"Cam over" in itself has no meaning. You set the sizing die up based on the fired case datum line measurement (primer removed) and size to .001 to .002 shoulder set back IF the shoulder needs set back. Otherwise, set it up for a zero set back. The amount of slack in the press linkages will determine how much, if any "cam over" is needed to achieve the desired sizing.
Some variation in measurements can be expected based on operator / caliper error and brass consistency especially if you don't anneal. But even without annealing, .005 seems excessive or at least I've never experienced that amount of variation, but I use virgin casesdedicated to a specific rifle and rotate their use.
"Cam over" in itself has no meaning. You set the sizing die up based on the fired case datum line measurement (primer removed) and size to .001 to .002 shoulder set back IF the shoulder needs set back. Otherwise, set it up for a zero set back. The amount of slack in the press linkages will determine how much, if any "cam over" is needed to achieve the desired sizing.
Some variation in measurements can be expected based on operator / caliper error and brass consistency especially if you don't anneal. But even without annealing, .005 seems excessive or at least I've never experienced that amount of variation, but I use virgin casesdedicated to a specific rifle and rotate their use.
Always.
Yep, that too.
A partial turn of brass and a repeat also helps with uniformity.
DLT
Silver $$ Contributor
I have never seen a need to as far as seating bullets. What does the dwell time do for that ? Not bucking you just want to try and learn
I’m sure glad that someone besides me does this.
DLT
Silver $$ Contributor
I sure do it. Have always done it
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