Reloading dies are special tools that are fixed into the tool head of the
press and are specific for each calibre.
There are 6 basic functions of dies: de-priming, sizing, powder charging, expanding, seating and crimping.
The sizing and depriming functions are usually combined in one die, where the case is cleared of the old primer and sized to factory dimensions. The sizing is performed either on the entire length of the cartridge case (full length sizing) or just a neck only (collet/neck sizing dies - available only for bottle cases).
The expanding and powdering function is most often combined in pistol calibre dies. The purpose of the expanding function of the die is to create a slight flare on the neck of the brass case to make it easier to seat the bullet. During this operation, the case may also be charged with gunpowder using either attached automatic powder dispenser, or manually through attached powder funnel.
The seating die is used for the accurate seating of the bullet in the cartridge case. The use of a proper seating die ensures that the bullet is always properly seated on axis and at a consistent depth. Some seating dies also offer a crimp function, but we recommend using a separate die for this step if available.
The crimping die crimps the bullet in the case. This die is an absolute
must if you will be using the ammo in a self-loading gun. It is also recommended
to crimp cartridges loaded into a magazine. In addition, proper crimping
improves accuracy, because the pressures in the cartridge needed to push the
bullet out are higher. Increasing the pressure at the beginning of the shot
ensures more consistent burning of the powder, more balanced pressures in
individual shots, and thus more constant bullet velocities.
A special type of crimp die is the LEE Carbide Factory Crimp Die, which crimps the bullet and re-sizes the whole case with carbide sizer, so that each bullet is safely chambered with the reliability of a factory product.