The Lyman™ Black Powder Cartridge Taper Crimp Die 40-65 WCF, 40-70 Sharps require compression for proper ignition. This requires firm neck tension to hold the bullet without damage. The Lyman Taper Crimp Die has a minimum taper that allows the reloader to apply the proper neck tension without damaging the bullet, which results in the best accuracy. Shellholder sold separately.