Size unfired brass???

[Eagleye]

I never FL resize new brass, but will run them through a neck die if the case mouths are dented,
or to even neck tension if there are obvious issues.
Quite often, I just run the necks over the expander button to make them round so I can inside chamfer.
This has been working for me for 50+ years, so don't see a reason to change.
Eagleye.

 

[Dogleg]

You can add to this that all brass wears out, and the usual way is for the necks to crack. The necks crack from being sized down, then expanded as the sizing button is pulled through.
Thus, if you get 20 reloads from the casese, you lost 5% of the brass life by sizing.
If you average ten reloads, you have just taken 10% away from the life of your brass, by needlessly sizing it.
As has been pointed out, it is the same brass the factory loads their loaded rounds in, so what makes you think yours needs resizing?

I usually lose my cases to loose primer pockets before split necks, so it is of little concern to me.

 

[ykkid]

I'm thinking that if you can finger-seat a bullet in a factory new case, maybe there is a case for sizing. At least neck-sizing, and while you are at it, why not run it through the whole F/L die? If the factory case is spec, it won't touch the die. If it is under spec, it will wobble in the die. And if it is as oversize as a finger-seat neck is, it might give chambering problems if not intitially sized. As for working the case neck and using some unknown percentage of case life, well, life is full of compromises.

Sure, some of the absolute accuracy nuts essentially seat the bullets by hand - although they use a press to ensure minimal run-out, but for use in an AR, or any field use, a bit of neck tension can be your friend. Not to mention varying neck tension as a step in accuracy load development, but by then you will be using bushings, neck-turning, and a whole bunch of other esoteric practices.