That's what i love about these forums- you learn so much. So the brass was fired in a fat chamber and the "headspace" shrank? That's not been my observation at all. (e.g. machine gun brass) But, oh well. So now you take this fat cartridge case with the short "headspace" that already fits your chamber and FL resize it. Oh, Oh.
If it fits your chamber easily now, your sizing die probably won't size the case at all. Oh yeah, I forgot how the expander stretches the case when it comes out. Maybe that'll improve the headspace fit. Ooops! That rarely happens. I forgot. And as someone who once sized 7.62x51 machine gun brass with and without an expander and then checked both the headspace fit AND the OAL and found no discernable difference between the lots, I throw down the anti-laziness gauntlet and challenge others to do the same. Not 1 or 2 but say 50 of each. Please measure the "headspace" before and after and the OAL also. (for you purists- I know that headspace isn't measured on brass but it is a much handier term than datum envelope or some such)
And just for a philosophical point, I believe the OP was planning on comparing notes with others just to see if his idea/ideas were in line with others on the forum. And to Hondo 60, that snippy little comment was even less High Road than this snippy little comment.
So, Parker 51, my advice to you is to get a case gage, try a few with neck sizing only, try a few with full length sizing and see which is more apropos. I'll wager at least 50 cents that you'll be happy with the neck sizing. And think of all the money you'll save on lube.