Dead Length Bullet Seating Explanation

The idea behind the floating bullet seater plug or “dead length bullet seating” is as follows; If you look inside the bullet seating die, you will see a restriction about 3/4 the way to the top of the die. This restriction is only .001 larger than bullet diameter, and is positioned so that when the bullet starts to seat into the case, the bearing surface will be passing through this restriction.

The bullet seater plug, being free to move axially, and due to the shape of the cavity will find the center of the nose, and a properly prepared case will find the center of the base of the bullet. The die should be turned in to touch the shell holder and is designed to be adjusted that way to eliminate clearance in the press for a more uniform bullet seating depth.

Most case/bullet alignment is determined in the resizing die. If the case neck is sized too small, the bullet will actually resize (open back up) the case neck when it is seated. If the case neck is thinner or softer on one side (and they usually are) the bullet will push out more on that side. Excessive crimp or an out of square case mouth can also cause bullet run out.