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Verifying. Measuring fired case shoulder setback for a given die position in the press. Been there, done that in trump suit and took all the chips every time. Especially after I did all the right stuff.
First time I did that, I moved the die's lock nut around the die about 15 degrees to change die height down by 3/1000ths of an inch. Full length sized five .308 Win. fired cases after that and their case headspace ranged from 1.627" to 1.631". Chambering the longest one had the bolt binding the slightest amount when closed; evidence to me that headspace was somewhere between 1.6300" and 1.6310"; what my 'smith had stated it was.
Sized 10 more fired cases with the same results and then some. Then I got to thinking about how much spring the RCBS Rockchucker press has and what caused the 5/1000ths spread in sized case headspace; way too much for good accuracy. It finally dawned on me; lubricity of the case in the die. I was using RCBS or some other standard thick case lube on an old RCBS case lube pad. And not paying too much attention as to how much lube went on the cases.
After trying varying amounts of lube on fired clean cases, those with the greatest amount of lube got pushed further into the full length sizing die setting the fired case shoulder back the most. Cases with just a smidgen of lube had minimal shoulder set back.
Solution was to figure out how to lube the cases uniformly. Sierra Bullets' ballistic tech suggested I try a home made lube having a 50-50 mix of Hoppe's No. 9 bore cleaner and STP engine oil treatment and somehow tumble the cases to lube them. I cut a piece of 3/8ths inch thick soft foam sheet to fit a coffee can I used to tumble cases in with rice and BB's to clean cases, put 10 drops of my new home made case lube on the foam, put in 40 cleaned cases then tumbled them for 20 minutes. Dumped 'em out, full length sized every one then measured their case headspace.
1.6280" to 1.6295"; a 1.5 thousandths spread. Good enough for excellent accuracy.
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