What is a "Dead Length Seating Die"?

[Twmaster]

I'm looking at the differences in some die sets offered by Lee. One set includes a bullet seating die called a "dead length seating die".

I found some info via a Google search but frankly I did not get it.

So please, in simple language, explain this.

Thanks!

 

[Rod Snell]

For long-range bolt action rifle target shooting, special dies are used to load ammo so the case is fire formed to the chamber and the bulllet is seated to touch the beginning of the rifling. There is no crimp.

When the case and bullet exactly fill the chamber to the rifling, that is "dead length." Most ammunition leaves a "free" gap the bullet must cover to engage the rifling. The bullet can also be "jam" or "interference" fit if the bullet is forced into the rifling when the bolt is closed.

The dead length seating die is made to facilitate seating the bullet to exactly touch the rifling with no crimp or distortion of the case itself.

This whole esoteric process requires the use of the exact same rifle (some even mark the case so the same side is up each time), and the case is only lightly neck sized between loadings. Some custom bench rifles have very small throats and the cases are precision neck reamed so that there is no sizing between shots.

Not something appropriate for ordinary rifles and ammunitiion used for hunting, as the bullets are only lightly held in the cases.

 

[Twmaster]

Thank you. Very informative.