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Old October 15, 2012, 09:48 AM   #19
F. Guffey
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Join Date: July 18, 2008
Posts: 2,671
Bart B. says:

“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”

Memory work, etc., purchase all the tools, then there is another tool to purchase for another and or different chamber...?

Working backwards, after making all of Bart’s adjustments, VALIDATE! Validate the adjustment, after thinking about the validation process ask yourself why not start with the validation tool, use the tool to make the adjustment first, skip all the memory work and the ‘step-sequence’ go straight to the feeler gage/thickness gag.

“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”. The shoulder reference Bart is referring to is .400” the .400” is not a line with an arrow pointing to it and identified as ‘DATUM LINE’, The .400” reference is a round hole, for those that do not understand ‘measured from’ there are tools to purchase, expensive tools, tools that are nice to have but not necessary, for the rest of us there are savings.

Again, I make tools, I am not hard headed, the reference to datum with an arrow is not for reloaders, reloaders that do not understand the datum line post pictures with a line and arrow pointing to ‘DATUM LiNE’, a word or group of words with no meaning, anyhow the datum as in ‘reference’ is a hole, a round hole that is used to measure the length of a case from the round hole to the head of a case. it is not the hole the measurement is taken from but the plain of the plate the hole is drilled through. AGAIN: Do not put a radius on the hole, the radius lowers the .400” datum, datum? as in measured from.

Then there is me, no memory work, I do not have to keep up with the .400” hole as the reference when we talk about ‘measured from’, I do not have to keep up with the reference .375” hole that is used as the ’reference’ measured from for the 30/06 family of cartridges including the 7.7 Japanese etc.. Those that understand the term ‘measured from’ do not need the RCBS tool, they do not need a tool that is mistakenly marketed as a ‘head space gage’ because? The tools sold as head space gages are comparators.

I do not measure head space, I measure the length of the case from the head of the case to the shoulder of the case, I have two ways of accomplishing this task, one I can and do use a shoulder that is conveniently cut into a chamber gage or a tool like the L.E. Wilson case gage, the Wilson case gage has a datum, the datum of the 30/06 case gage is .375”, the Wilson case gage datum has a radius, the radius contact point between the gage and shoulder is .375”. OR! I can drill a hole straight through a plate or cylinder, the hole can be .375”, for those that can not drill a hole or fail to understand the ‘DATUM, as MEASURED FROM’ can purchase a case comparator labeled ‘head space gage’. Anyhow, I make gages.

Reloaders, trying to get Sammie to agree with the manual to agree with their chamber to get their chamber to agree with their dies... WHY!? In the big inning we started with the comparator, then a reloader started posting pictures with an arrow pointing to ‘DATUM LiNE’, there is no line, the line is making reference to ‘measured from’. Back to the .400” and the .375”, a reloader that understands measured from and understands this is not about head space but the length of the case from the head of the case to the shoulder and length of the chambers from the bolt face to the shoulder of the chamber understands without SAMMIE they can compare the length of a case before it is fired from the head of the case to its shoulder and measure again after firing to determine the effect the chamber had on the case.

THEN, one day someone with have one of those moments, all alone and by them self there could be a relation between the difference in length between the unfired and fired case that that could be used to adjust the die to the (or off the) shell holder. It works for me, I choose to off set the length of the chamber with the length of the case when measured from the ‘usual places’. Again, I have a 30/06 chamber that is .016” longer from the bolt face to the shoulder of the chamber, that a minimum length, new, store bought, factory make ammo, when sizing cases for that chamber I adjust the die opff the shell holder .014”, that cuts down on all that case travel, me? I am the fan of cutting down on all that case travel.

It is not necessary to use .400” (reference) for the 308W family of chambers, It is not necessary to use .375” (reference) for the 30/06 family of chambers, it is necessary for a reloader that choose one or the other to understand why it is not necessary.

And I make gages, I have sent 4 sets to reloaders, collectors and machinist that were fair and objective, the go-gage was the most useless in their opinion, the most useful was the the one that matched their maximum acceptable length for a chamber.

F. Guffey
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