What exactly does neck tension do? Why is neck tension nessessary? What creates the force against the bullet while trying to seat it?
Brass has 'spring', it has a memory, it doesn't like to change, so, as you seat a bullet, the brass expands, but at the same time, it's trying to go back to the size it was. This sprinyness is what holds a bullet. The amount of force it takes to expand the brass, does not mean that's how much force is being applied to the bullet.
This characteristic of brass is the reason it work hardens, as work hardening sets in, the brass loses it's spring and therefore has less tension on the bullet even though seating force is increased.
If you read the article on accurateshooter, you will notice ge talks of seating force, but does not quote any figures.
As I said previously, the only way I get consistent tension, is to anneal the necks every other firing for my comp rigs. My hunting rifles I just do 3 different bushing sizes starting at .002" and going up in size to .003" and .004", whichever gives the best groups is what I use. Also, if I use an expander, they get polished and I always use powdered graphite brushed inside the necks. My hunting rifle brass gets annealed every 4th firing prior to sizing.
Cheers,
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