When I measure a fired case at the shoulder (with Stoney Point Gague) it measures 3.895". I want to set the shoulder back .001"-.002". When I full length size it measures with gague at 3.896". Should it not size back to 3.894" or am I just confused? Am I doing something wrong?
setting shoulder back
- Thread starter dbaird
- Start date
David Halblom
Flying Fish Fundamentals
Odds are that the die is still not set right. If the shoulder grows in length, the die is not touching the shoulder area and as a result the movement in the brass is to a longer shoulder. as you squeeze the case, the brass will move to the point of "0" resistance. If you are talking a factory chamber and a off the shelf die, you could well have a short chamber and a long die.
Spring in the press frame or spring back in the brass if not moved back far enough to start.
Can you see light between the ram and die with a case in the holder and the ram at TDC? You need to seat deeper if so.
Are you lubeing the case mouths? Shoulders can be "pulled" forward by the expander ball if drag is heavy enough.
Lots of things can cause the case to "grow".
Can you see light between the ram and die with a case in the holder and the ram at TDC? You need to seat deeper if so.
Are you lubeing the case mouths? Shoulders can be "pulled" forward by the expander ball if drag is heavy enough.
Lots of things can cause the case to "grow".
Boyd Allen
Active member
Pretty typically, if you are adjusting a die down, a little at a time, looking for the desired degree of shoulder bump, you will pass through an adjustment range where the diameter of the body of the case is being reduced, but die is not far enough down for the case shoulder to come in contact with the corresponding part of the die. As the body of the case is reduced the unrestrained shoulder moves outward, producing "negative bump". Then as the die is brought farther down the shoulder of the die starts to have an effect on the shoulder of the case, and eventually desired degree of shoulder bump is achieved. Once this adjustment has been achieved, several more cases should be checked to see if they have the same measurement. Pretty typically, there will be some variation, and the range of measurements is too great, some cases will require more bolt closing effort when chambered. When this happens. It will be slightly detrimental to accuracy.
First, make sure you remove the primer from the fired case when you measure it. It can add .002-.003 thou to your measurement.
It's not unusual for the case head-datum dimension to get a couple thou longer just before the shoulder starts to get pushed back. And you may need to make pretty hard contact with the shell holder to the bottom of the die to take all the slop out of the system and let the press 'cam over'. -Al
It's not unusual for the case head-datum dimension to get a couple thou longer just before the shoulder starts to get pushed back. And you may need to make pretty hard contact with the shell holder to the bottom of the die to take all the slop out of the system and let the press 'cam over'. -Al
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I have a just-in-case question, because you didn't say: can you chamber the case that measures 3.896 after sizing? If so, your assumption it should be .001 shorter than 3.895 is wrong. If not, the others have given good advice on how to proceed.
A
abintx
Guest
Could be, since the measurement should be 3.894" to 3.893" with a deprimed case. If you're using the full length die with that "darn expander ball" get rid of it, or at least remove it and put in a drawer for eternity. Then see what happens. Those darn things can undo what you're trying to accomplish, even more so, with a full length die that uses bushings.
Here's a Digital Headspace Gauge that really helps because it uses "gravity as a constant" vice "person power" [which varies], to assist with the measurement: http://www.larrywillis.com/
Boyd Allen
Active member
One little tip: In the past, I have decapped fired cases to make sure that a small primer crater, did not ruin the accuracy of my before sizing measurement, then it finally dawned on me. Now I just put the case back in my hand priming tool, which is always handy, and reseat the fired primer well below flush.
goodgrouper
tryingtobeabettergrouper
Just to clarify, DON'T get rid of the expander ball if you're using a standard FL die! Only get rid of it if you're using a neck bushing FL die.
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abintx
Guest
dbaird,
Normally I might agree, depending on the numbers you're working with. However, since the shoulder is only being pushed back the infinitesimal amount of .001" to .002", the inherent design of an expander ball can easily overcome that measurement, as it accomplishes what it was engineered to do [straighten out necks], by expanding the neck and as an unintended consequence dragging the shoulder's material along with it, in the opposite direction.
Just to keep things in perspective, .001 to .002" is so small, I've never been able to see it, only measure it. Take a piece of copy paper, turn it sideways, that's .004". We're talking 1/2 to 1/4 of that thickness.
OK, don't get rid of it. Put it in a drawer and leave it there. Or, turn the ball down until it doesn't overcome your intended headspacing.