Dies
Dies are generally sold in sets of two or three dies, depending on the shape of the case. A three die set is needed for straight cases, while a two die set is used for bottlenecked cases. The first die of either set performs the sizing and decapping operation. The middle die in a three die set is used to expand the case mouth of straight cases, while in a two die set the entire neck is expanded as the case is extracted from the first die. The last die in the set seats the bullet and may apply a crimp. Special crimping dies are often used to apply a stronger crimp after the bullet is seated. Progressive presses sometimes use an additional "die" to meter powder into the case (though it is arguably not a real die as it does not shape the case)
Standard dies are made from hardened steel, and require that the case be lubricated, for the resizing operation, which requires a large amount of force. Rifle cartridges require lubrication of every case, due to the large amount of force required, while smaller, thinner handgun cartridges can get away with alternating lubricated and unlubricated cases. Carbide dies have a ring of tungsten carbide, which is far harder and slicker than tool steel, and so carbide dies do not require lubrication.
Modern reloading dies are generally standardized with 7/8-14 (or, for the case of .50 BMG dies, with 1-1/4x12) threads and are interchangeable with all common brands of presses, although older dies may use other threads and be press-specific.
Dies for bottle neck cases usually are supplied in sets of at least two dies, though sometimes a third is added for crimping. This is an extra operation and is not needed unless a gun's magazine or action design requires crimped ammunition for safe operation, such as autoloading firearms, where the cycling of the action may push the bullet back in the case, resulting in poor accuracy and increased pressures.[9] Crimping is also sometimes recommended to achieve full velocity for bullets, through increasing pressures so as to make powders burn more efficiently, and for heavy recoiling loads, to prevent bullets from moving under recoil. For FMJ bullets mounted in bottle neck cases, roll crimping is generally not ever used unless a cannelure is present on the bullet, to prevent causing bullet deformation when crimping. Rimless, straight wall cases, on the other hand, require a taper crimp, because they headspace on the case mouth; roll crimping causes headspacing problems on these cartridges. Rimmed, belted, or bottleneck cartridges, however, generally can safely be roll crimped when needed. Three dies are normally supplied for straight walled cases, with an optional fourth die for crimping. Crimps for straight wall cases may be taper crimps, suitable for rimless cartridges used in autoloaders, or roll crimps, which are best for rimmed cartridges such as are used in revolvers.[9]
There are also some specialty dies worth mentioning. Bump dies are designed to move the shoulder of a bottleneck case back just a bit to facilitate chambering. These are frequently used in conjunction with neck dies, as the bump die itself does not manipulate the neck of the case whatsoever. A bump die can be a very useful tool to anyone who owns a fine shooting rifle with a chamber that is cut to minimum headspace dimensions, as the die allows the case to be fitted to this unique chamber.[10] Another die is the "hand die". A hand die has no threads and is operated - as the name suggests - by hand or by use of a hand operated arbor press. Hand dies are available for most popular cartridges, and although available as full-length resizing dies, they are most commonly seen as neck sizing dies. These use an interchangeable insert to size the neck, and these inserts come in .001 steps so that the user can custom fit the neck of the case to his own chamber or have greater control over neck tension on the bullet.