The standard set of 3 dies for 38/357 uses a modified roll crimp in the bullet receiving die. It's good and hasn't let me down, but I wanted a very strong crimp for my full power magnum loads. You are limited by the amount of crimp you can use on the landing die. Compressing too much will try to push the bullet down after it starts compressing, causing the case to warp. This is most common on federal brass. The factory die allows you to set the adjustment die to a standard crimp and then do a full taper crimp once the ball is seated. This eliminates hull distortion. It also pushes the modified roll crimp further away from the landing die, leaving a perfectly tight crimp every time. The crimp is sturdier than most factory chucks. I also have a factory die for my 45 ACP setup. The only downside to using a factory die is that it offers a little more resistance to leverage if you're using a progressive press. I use a 5 die setup (excess sizers) and it takes a little nudge to complete each cycle. It's worth it if the ammo is better than factory stock, which can fire at over 300 rounds per hour.