http://www.charm.net/~kmarsh/788.html
F. Guffey
"Full length sizing will create excess headspace if the die is screwed down too far and pushing the shoulder back.
Maybe that's your problem"
If the die is screwed down to the shell holder (far enough) it is called full length sizing, that is sizing a case that is the same as an over the counter, new, store bought, commercial size ammo, I only have one version of full length sizing, after that I allow the very versatile full length sizer die produce custom sized cases that fit the chamber with the aid of the companion tool to the press, the feeler gage.
But, I start by sizing cases to the chamber as in form first, then fire, others fire first then try to determine what happen.
The 243 is a 308 is a 30/06, or the 243 is a 308 that can be formed from a 7mm57, 8mm57 or the 7.7, no matter what case I look for a case that is too long from the head of the case to the shoulder, by forming the case and moving the shoulder back head space can be determined without firring, knowing when to stop moving the shoulder back is the key, and knowing the case being formed is not going to be fired but used as a transfer and or for those that can measure the length of a case from the head of the case to it's shoulder in thousands ( or measure the length of the case for the effect it has on head space).
There is full length sizing, then there are all the other options, for most it is full length sizing or neck sizing, I have as many as 10 options between full length sizing and neck sizing, with the versatile full length sizer die.