“So, let's say I have some fired cases, a FL die, a shell holder a press, and a Hornady "headspace gauge", and I am about to set the dieâ€
If I may be allowed a liberty, and say I am allowed to disagree on a few points? I would say Hornady makes a comparator they mislabeled as a head space gage, I would also suggest firing the cases was not necessary, and I would suggest the trip to the range would be a good thing the trip was not necessary when determining the length of the chamber because you have a press, die and shell holder, to deterring die adjustment (to, below or off the shell holder you could use cases that were to long to chamber.
Case forming and determining the length of the chamber, I have a 308 W forming die, I form 308 W cases from 30/06 cases, I can not miss when getting an absolute fit between the formed case and the chamber. The 308 W is shorter than the 30/06 from the shoulder to the head of the case by .389â€. And, no, I am not obligated to load and fire the cases, again, I want to know the length of the chamber before I fire, not after, then there is verifying, with the/a comparator I could measure the case after firing.
“dies that don't size enoughâ€
I am not an assumer, I do not assume the press, die and shell holder sized the case when the ram is/was raised. Again, reviewing this thread, there is sized, not sized enough, too much, and anyone's guess. Reloading does not have to be that way, without all the bench top tools/equipment a reloader can determine if the case was sized to minimum length/full length sized. Back to ‘not assuming’, before lowering the ram a reloader can check to see if the die made it to the shell holder, if not there will be a gap between the die and shell holder, the gap represents the amount of case that did not get sized, the gap also represents the amount of press flex created by the case’s ability to resist sizing, in the perfect world new-unfired cases would be used, after that once fired cases would be used. At some point the resistance of the case being sized must be considered.
Instructions: Starts with: (something like) Screw the die in until it contacts the shell holder ‘with the ram up’, then lower the ram and give the die an additional 1/4 turn. The instructions do not continue with additional instructions ‘like’ if the first attempt at sizing the case is unsuccessful turn the die down an additional 1/4 turn, again, the additional turn of the die into the shell holder is a means of overcoming the cases ability to resist sizing, and at the same time increasing the flex of the press.
Like others, I have presses, some were guaranteed not to flex, the guarantee says nothing about braking the handle in the effort. Sinclair/Hornady head space gage? OR, Sinclair/Hornady comparator, The Horandy/Sinclair or any other tool that measures case length is not a head space gage. When using a comparator the reloader is comparing a before and after measurement on the case from the shoulder/datum to the head of the case, the difference between the two measurements indicates the effect the chamber had on the case when fired. The comparator measure case length from the shoulder/datum to the head of the case, SAAMI does not list head space on the case, SAAMI list case length, normally with a –.000†number, SAAMI list head space on the chamber (almost?) always with a minimum and maximum in .000â€.
As you said, you fire a case, then measure, there are a few that measure first and then fire, it is possible to form cases before firing, by knowing the length of the chamber first the reloader can adjust the die to size cases to fit the chamber from the shoulder to the bolt face, convincing someone that is possible can be difficult. Not a route I recommend because it can be expensive, I have at least 15 forming dies, not necessary for most sizing jobs. When determining the length of the chamber first I use cases that will not chamber as in being too long and or a case that requires forming. The favorite case is the 280 Remington, it is .051†longer than the 30/06 family of chambers from the shoulder to the head of the case, my opinion, it is a can not miss option. Then there are cases fired in trash ole chambers, I have purchased thousands of them at gun ranges for $8.00 for 110. I simply measure the length of the cases from the shoulder to the head of the case, many times I have been able to match them in groups of 20, again, the long cases are tools, I am under no obligation to size the cases and fire them, I want to know the length of the chamber, I find sizing/forming is easier than making a trip to the range to fire to form then measure.
Then there is case forming, neck the case up to .338†or .350†then start necking the case down, eventually a new shoulder will be established, all a reloader has to do is be able to keep up with the distance from the new shoulder to the head of the case. Moving the shoulder or bumping, I can not bump, with the extremes of sizing and or forming the shoulder is erased, the shoulder does not move it stays put, the shoulder that is formed is a new shoulder, no one scribes the location/position of the case body/shoulder junction, I have, the scribed line does not move.
F. Guffey