Overview

This is a hand tool that uses a standard small boxcutter blade to trim a configurable length off the end of an empty shotgun hull (what many call a “shell”). If you want to trim the ends off of loaded cartridges, see https://www.printables.com/model/698822

This is done to cut new, empty hulls to the correct length, or to trim the crimped end off a once-fired hull so that it can be roll-crimped closed without mangling the end of the hull.

Printing & Assembly

Print the file without support. It should contain three objects: Two Handles and a cylindrical Stop. To assemble you will also need:

1 off M5 screw at least 25mm long

2 off M5 Washers (optional)

1 off M5 nut (preferably a lock nut)

1 off M3 screw at least 35mm long

1 off M3 nut

1 off M3 washer (optional)

4-segment length of small (9mm) boxcutter blade

Take the Handle with the biggest projection out the side ("Bottom Handle") and look underneath it for the hexagonal hole. M3 nut goes in the hole.

Place the cylindrical Stop in the matching trough in the top side of the Bottom Handle, smooth side down. Put the M3 screw (and optional washer) through the slot in the top of the Stop. Screw the Stop to the Bottom handle through the hole with the nut at the bottom of it.

Put the Top Handle against the Bottom Handle so the the cylindrical troughs match up, making a tunnel.Put the M5 screw (with optional washer) through the Handles' pivot holes from the left side. Secure the M5 screw with nut (and optional washer).

Take the length of Blade, and carefully place it in the slot in the Bottom Handle sharp edge up. It will leave 2-3mm of exposed blade when in place. If it is a little loose, pack with adhesive tape on the side of the blade. Assembly is now complete. When the blade becomes dull, push it out with a punch or nail from the other side of the handle and replace it.

Setup & Use

Loosen the M3 screw slightly so that the Stop can move. Decide where you want to trim your shotgun hull, and - open end first - line that point up with the blade. Adjust the Stop so that it rests on the open end of the shotgun hull. Tighten the M3 screw so that the Stop will not move when the hull is pressed against it.

Open the two Handles and place the hull between them, with the open end hard up against the Stop. Close the two Handles together. With some hulls it is best to gradually close the handles while turning the hull, and with others firmly keep them closed from the start. Only experimentation can tell.

With even motion and moderate pressure, rotate the shotgun hull by its base through at least one revolution. It is important to use even pressure and smooth movement, and keep the hull straight. Push too hard and you distort the plastic of the hull. Push too softly and the cut will try to spiral outwards. You will wreck a few shells determining the ideal pressure.

There is a slot for another blade in the top handle, it's not used but I left it there in development and someone might find a use for it. Also, if you take the Stop off, you can cut the shells - sorry, hulls - anywhere you like.

When you feel the hull come apart, open the handles and remove the cut-off crimp. As always, check the hull for splits and defects before loading the noisy stuff inside…

The OpenSCAD source file is provided, and should adjust for other calibres.