Editing Handloading (section)

===Crimping Dies ===
Sometimes die sets include a separate die for crimping and this is done as an extra operation.  There are two types of crimp, roll and taper.  Crimping is required for several reasons such as autoloading firearms, firearms with a tubular magazine or pistols with massive recoil (.500 S&W), where the cycling or recoil of the firearm may cause the bullet to move in the case,  resulting in poor accuracy, increased pressures or malfunctions. Some reloaders will only crimp only if absolutely necessary.

Roll crimping is usually appropriate for everything except cartridges that headspace on the case mouth (I.E. 9MM and .45ACP).  Magnum straight wall and bottleneck cartridges ar usually roll crimped.  Bullets that require roll crimping usually have a cannelure on the bullet, this prevents bullet deformation when crimping.

Cases which headspace on the case mouth, on the other hand, require a taper crimp, because they require a flat surface at the case mouth; roll crimping will cause headspacing problems on these cartridges.