Lee, I use a drill press with a dowel that is the right diameter for 10 ga. 12 ga, 16 ga. and 20 ga. Just set the stop to the length you want and move the cutter towards the rotating hull and cuts it clean as can be. It is a box cutter mounted in a piece of 1 1/2" x 1 1/2".
These happen to be 20ga. Rem, being cut to 2 1/2" and then I roll crimp all sizes.

David