Shotgun Shell Crimp Remover (parametric 12ga, 20ga, 28ga)

This is a device that neatly trims the crimped tops off loaded 12 gauge shotgun shells. There are separate model for 20 gauge and 28 gauge. Mostly this is done to reload shot shells with the appropriate solid shotgun slug, such as the Lee, which fit inside a standard shot cup.

Components

As well as the 3D print parts, you will need:

3 x M3 Screws, between 16 and 20mm long

3 x M3 Nuts, ideally lock nuts

1 piece 9mm (3/8") box cutter blade snapped off to 20mm long (4 segments). All models use the same sized blade.

Printing & Assembly

Print the model in the chosen gauge with at least 25% infill. PLA is up to the task. They should print without support or brim despite producing warnings. Ensure plunger is loose in the top section and insert a nut into each cavity in the side, which will require a screwdriver or needle nosed pliers. Use a probe (2mm drill bit works well) to ensure each nut is centred over its corresponding hole in the base.

Note: The nuts need to be inserted with their flat sides parallel to the edges of the hole. Do not be fooled by the curvature of the textured surface! Test with a screw to make sure the screw actually lines up with each nut.

Place the blade segment into the cavity in the base, sharp edge in the central hole, and sandwich it with the top section. It may be helpful to use a small piece of tape or glue to make sure the blade does not slip during assembly.

One at a time, drive the M3 screws through the holes in the base into the captive nuts. You will probably need to re-tighten after the first use.

Use

Wearing stout gloves, push the shotgun shell into the hole in the base as far as it will go. Do not push the plunger yet. 

Keep pushing firmly and rotate the shotgun shell 3-4 times, always going in the same direction. A slight pull may be needed to complete the removal of the top of the case.

When the shell case separates, hold the device over a bowl and pull the shotgun cartridge out. The shot will pour into the bowl (and occasionally onto the bench). Smack the plunger sticking out the top, and the crimp from the shell case will be ejected. Rinse and repeat.

Why?

I use this for Cowboy Action shooting (known as CAS or SASS) for two reasons: I can cut down the shot load to lessen recoil, and the shorter shotgun case (when roll crimped back together) comes out of the shotgun quicker - cowboy shotguns do not have automatic ejectors.

I have also used this to render dud shotgun cartridges inert, and to cut down 2 ¾" shotgun shells to fit old 2 ½" English shotguns.

Notes:

The OpenSCAD model is parametric, and I have included a suggested diameter for 12, 20 and 28 gauge shells, though you can make others to suit. You may wish to enlarge the screw hole diameter to fit 1/8" screws (and the nut size) if you can't get metric. If you need this and can't do it, comment below and I'll upload models for imperial.

As with all ammunition loading, always follow the manufacturer's loading data and if possible seek the advice of experienced shooters. Wear a mask when handling lead shot, and wash afterwards.