^ this.
Redding 3 die sets will have a neck size die that only squeezes the neck down, leaving the case body fireformed to fit your chamber. This is a step beyond entry level reloading.
Lee sends 4 dies in their kits. The 4th is a "factory crimp die" that crimps the case mouth into the sides of the projectile to keep it from moving if the loaded ammo get heavily jostled around. There's some debate on crimping rifle ammo. I crimp all my bulk plinking ammo. Anything for an AR should be crimped in my opinion. The factory crimp die for pistol, straight walled case forces the entire round into shape, making for easier chambering. Some feel it can crush the projectile too much, I haven't seen an issue and run all rounds through one.
Get a dedicated decapping die from Lee. Then you can deprime and clean up your brass prior to running it through the size die.