I've cut hundreds of .284 Win cases off to make .450 Bushmaster using my full size chop saw. First drill the appropriate diameter hole through a block of Hardwood, then screw it to a board so you can clamp it to the table at the correct final, (nearly final), length using a shell holder to index the case, and cut through the block and the first case. The block supports the case wall giving a very clean cut. After that I just push in a new case and zip them off. I used an 80 tooth finish blade and it worked fine. Takes about two seconds per case. Sorry about the sideways pic. No idea how I managed that.