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Old October 11, 2012, 02:14 PM   #13
Bart B.
Senior Member
Join Date: February 15, 2009
Posts: 6,169
Brokenanew asks:
Soooo, How do I adjust the die and measure the bumping of the neck. Thats all kind of new to me really. I just put the die in until it meets then screw in a quarter of a turn. How do I measure the bump of the shoulder? How do I adjust accordingly?
You'll need a gauge that measures the distance from case head to shoulder reference (RCBS Prec. Mic, Hornady, etc.) to measure what a fired case headspace is. That's the length from the case head to a reference point on the case shoulder. Then adjust your full length sizing die in the press to set the shoulder back 1 to 2 thousandths. Note that 1/4 turn on your die changes its height about 18 thousandths. Adjusting the die such that its threads move 1/10th of an inch around the lock ring (about one 70th of a turn) changes it about 1 thousandth inch. This is all based on the 14 threads per inch the die has and that's about 71 thousandths of an inch between threads. 1 divided by 14 equals 0.0714 inch.

The die may well be set correctly such that it's bottom is a few thousandths off the shell holder. It all depends on several things with the press as well as the die's dimensions; these are not important. Wherever the die needs to be locked in place to set fired case shoulder back 1 to 2 thousandths is correct.

You'll notice that full length sizing a batch of cases then measuring the case headspace on each, the spread in measurements will be a few thousandths of an inch. That's 'cause of the spring back properties of the press and how much lube you put on each case. Try to get the same amount of lube on each case; very little is needed all over its outside to do well.

Last edited by Bart B.; October 11, 2012 at 07:58 PM.
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