As I understand it, to set the shoulders back I only need to slip a 0.5mm feeler gauge under the base of the case and operate the press as before.
You have confused everyone but me, math does that. .4mm is equal to 0.01968503 or close to .020". Problem, there is no shell holder that will allow a reloader to place a feeler gage that large between the shell holder deck and case head. the other area of confusion, shimming the case off the deck of the shell holders allows the reloader to size cases for short chambers.
Then there is the "BIG AND", and shimming the case head off the deck of the shell holder increases the presses ability to overcome the cases ability to resist sizing. It is beyond comprehension but shimming the case head off the deck of the shell holder has the same effect as a small base die.
My experience: The maximum shim I can get between the case head and deck of the shell holder is .012" for a RCBS shell holder and .015"+ for a Lee. When cutting chambers with a reamer use cases for short chambers to determine "How close I am to finishing", then of course, I verify.
Verify? With a head space gage that does not exist.
Then there is bump, again, that sounds like a accident. I can not bump the shoulder without bumping? the case body and bumping? the neck. the neck, shoulder and case body are attached with junctures. All of my dies are one piece. It does not have to be that way, reloadrs can purchases dies in pieces, they can purchase neck sizing dies, then there is body dies, there are bump dies etc. etc.. And there is confusion. I could have been using body bump the shoulder back dies for ever, I just never found it necessary.
Sizing a case, it starts with determining the length of the chamber from the shoulder to the bolt face. That is something reloadrs can not do. That leaves fire forming. Chamber a round, pull the trigger and then eject the fired case, instant gratification. The reloader has become a fire former.
After fire forming the case the reloader must learn to measure the length of the case. tools are available, most should be able to make the tools. When measuring the case the case is to be measured from the shoulder to the head of the case. For the 308 W the 'MEASURED FROM' is a .400" round hole circle called datum to the case head.
I suggest reloaders measure the length of the case before firing and again after firing. Measuring before and again after allows the reloader to understand the effect the chamber had on the case when fired. And still there are those that believe I am talking about the length of the case from the end of the neck to the case head. I am talking about off setting the length of the chamber from the shoulder to the bolt face with the case when measured from the shoulder to the case head. Back to knowing the length of the chamber before firing and cases that have been fired in trashy old chambers, Or as members on reloading forums like to say: "Cases that were fired in rifles with chambers that do not belong to you".
My favorite cases are cases that are long from the shoulder to the case head, I prefer cases that are .010" longer from the shoulder to the case head than new, over the counter, factory new in the box ammo. OR? Military loaded unfired, still in the can or fiber box ammo. Among my other favorite ammo is military fired, especially those mean ol' cases that have been fired in machineguns. I am the only one that measures before sizing, if that case is going to whip my press I want 'A HEADS UP'.
Whip my press? I have case forming dies, I have small base dies, I have dies that are mistakes. Dies that are mistakes will keep a reloader busy, sizing a case with a die that is a mistake is like sizing cases that have been fired in large chambers. A die that is a mistake could be called a very small base die.
Pulling stuck cases.
If a reloader could figure the length of the chamber the reloader could adjust the die to the shell holder by adjusting it to, or off and or below contact. Again, I size 280 Remington cases to 30/06 by adjusting the die off the shell holder .014" for a 30/06 chamber that is long from the shoulder to the bolt face. I know, there is nothing wrong with the chamber when it comes to case head protrusion or unsupported case head. The case head protrusion .025" less than the Mauser 98, Most case head protrusions for the Mauser 98 is .110+ case head clearance between the case head and bolt face.
F. Guffey