If you are using all the tricks of the trade to prep your brass and then shooting the ammo in an "off the rack" gas gun, I'm afraid you'll be disappointed and will probably be convinced till the end of time that it's not worth the trouble. You have to load your ammo in a way that best suits your needs.
If you load for a bolt action bench gun, you want to neck size only and have minimum shoulder set back, just enough that you can close the bolt, to achieve maximum uniformity. This can be accomplished in two steps with a Redding Competition Die Set with a separate body die and Competition Shell Holders that allow you to adjust the set back by increments of .002" from .002" to .01". These shell holders fit the ram of your press very tightly, and I find I have to tap them in place with a brass drift. It can also be accomplished in a single pass with a custom cut die that is designed to neck size and set back the shoulder by a predetermined amount.
If you are loading for a hunting rifle or a gas gun, function trumps accuracy, so you should full length resize to ensure that the action of the rifle will function. Will your gas gun and hunting ammo be less accurate? Yes, but the looser tolerances in those rifles make them less accurate than your bolt action bench gun. It doesn't hurt to cull out the heaviest and the lightest cases when loading accurate hunting or gas gun ammo, but to pick through hundreds of cases to find 100 that are identical in weight is kind of pointless, as is with neck turning, weighing primers and measuring the depth that you seat them, attempting to weight powder to a tenth of a grain, or seating your bullets with a hand die.
As to the problem you have experienced with the Lee seating die, I have experienced similar problems with other makes of dies from time to time. I don't waste a lot of effort worrying about it if I can use a longer seater stem from another die set or simply put some temporary filler material inside the nose of the seating stem plug.
Boomer, You always give great information, in easy to read and understand language, expressing a lot of experience. I sometimes also, write lengthy replies to some newcomer with a simple, to us, problem. However, I often wonder why I bother.
Almost never, does the person we are trying to help, by giving information based on many years of experience, ever acknowledge our help. The same is true of other very experienced people trying to help.
So many times I have seen another newby answer by saying he read something about that in a certain book, and the original writer will reply with something like, "Thanks for the information, I will get that book."
Just my thoughts and opinion.