As a general rule, roll crimps are recommended for most revolvers, rifles using tubular magazines and situations that call for an extremely high bulletpull. Taper crimps are normally best for straight-wall cartridges that headspace on the case mouth, particularly those to be used in an autoloading pistol. The object behind the roll crimp is to firmly grip the bullet, in order to provide better ignition and reduce the possibility of the bullets being “pulled” under recoil. Taper crimping, on the other hand, merely removes the case mouth flaring left by the belling/expanding operation. While this may also increase neck tension, the degree of improvement is relatively slight in comparison to a firm roll crimp.
How do I know whether to taper or roll crimp?
Sierra Bullets > FAQs > How do I know whether to taper or roll crimp?