[Unclenick]

I use my AR in match shooting and don't crimp except for occasional experimentation. It's not really necessary for my purposes.

For the roll crimp shoulder in your seating die, you want to be careful to get your cases all the same length and sort them by headstamp so the neck thickness is the same to the crimp is consistent. If you are adding a Lyman M expanding die to help bullets start in more straight, then you may want to buy a taper crimp die to iron the step out flat. The Lee Factory Crimp die doesn't require the cases to be quite so exactly the same length, but you still want the neck thicknesses uniform to use it.