It's basically a size die, cut of so that the case tops out at the trim length when the ram is all the way up. The top surface of the die is hardened so that a file won't cut it. Very easy to use; Run the die down to the shellholder so that it cams over slightly when it's at full extension, and lock the die with the die ring provided. After this, lube a case and run it up the die like you're sizing it. Leave the ram fully extended at the top of its stroke. For the trimming, use a single fine-cut file to remove anything to the case mouth that's protruding over the top of the die. Don't worry abou the die, this is why it's hardened; the file won't cut it. It will, however go through the brass in just a stroke or two. When the case mouth is flush with the top of the die, remove it. Use your deburring tool to chamfer and deburr the case mouth and you're good to go. repeat with all cases. You'll want to check the case length (of course), but these are pretty hard to get wrong, and virtually impossible to over trim with.
