Harbor Freight makes a mini-chop saw which in combination with a jig made by an Ebay seller is perfect for trimming hulls quickly, neatly and with precision. The jig clamps into the saw's adjustable jaws. I use one to trim 12 ga. hulls into 2" length. The Ebay seller will make the plastic jig to any length desired.
Here's the jig for .45 ACP, but if he is contacted, he'll make the jig for shotgun shells at the same price.
https://www.ebay.com/itm/New-45-Shot-Shell-Trimming-Jig-2-Chop-Saw-Safe-Scratchless-308-243-260-Brass/264391246256?hash=item3d8ef241b0:g:x~YAAOSwWHBdIo-H

Gil