The New Hotness

Having accumulated a box of empty 12 gram CO₂ capsules and having already done Too Many bomb fins:

The capsule is obviously the wrong shape, too short, and only 19 mm diameter, but it’s the thought that counts.

Apply the contour gauge to a genuine slightly battered 20×102mm cartridge:

Scan the sketch, import into Inkscape, rotate the image to correct the case taper angle vs. the page, lay lines & curves around the perimeter, align half of it at the page origin to work with OpenSCAD, export as SVG:

Cartridge - 20x102mm outline - Inkscape layout — Cartridge – 20x102mm outline – Inkscape layout

Import into OpenSCAD, let rotate_extrude do the heavy lifting, and remove some pieces:

Cartridge Case - build view solid model — Cartridge Case – build view solid model

The little disk represents a fired primer you’d print separately in a different color and glue into the pocket shown in this cutaway view:

Cartridge Case - cutaway solid model — Cartridge Case – cutaway solid model

The interior void could hold sand for additional heft, as the whole thing is obviously nose-heavy; that’s certainly in the nature of fine tuning. Obviously, we are not dealing with anything that could go bang.

It builds just like you’d expect:

20x102mm cartridge - printing — 20x102mm cartridge – printing

Dab some adhesive on the capsule tip, ditto for the primer, stick them in place, and it’s all good.

I like the gray PETG-CF version:

20x102mm cartridges - blue gray PETG-CF — 20x102mm cartridges – blue gray PETG-CF

Maybe not such a good idea in this day & age. Print responsibly, as they say.

Update

Print a sabot to fit a CO₂ capsule into a genuine steel cartridge.

The solid model:

Cartridge Case - sabot solid model — Cartridge Case – sabot solid model

The OpenSCAD making it happen:

module Sabot() {
tube(SabotOA[LENGTH],id=SabotOA[ID],od=SabotOA[OD],anchor=BOTTOM)
    position(BOTTOM)
      tube(SabotOA[LENGTH]/2,id=SabotOA[ID],od=CartridgeOA[ID],anchor=BOTTOM);
}

The result:

The OpenSCAD source code (minus the sabot) and outline as a GitHub Gist:

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view raw Cartridge – 20x102mm outline.svg hosted with ❤ by GitHub

	// 20x102mm cartridge
	// Ed Nisley – KE4ZNU
	// 2025-05-18

	include <BOSL2/std.scad>

	Layout = "Show"; // [Show,Build]

	Powder = true; // build internal void

	/* [Hidden] */

	ID = 0;
	OD = 1;
	LENGTH = 2;

	HoleWindage = 0.2;
	Protrusion = 0.1;
	NumSides = 334;

	$fn = NumSides;

	CartridgeOA = [21.0,29.5,101.4]; // must match SVG pretty closely

	PrimerOA = [2.0,8.0,2.0];

	CapsuleTip = [7.5,7.5,5.0];
	Capsule = [7.5,18.8 + HoleWindage,83];
	SeatingDepth = 25.0;

	Void = [CartridgeOA[ID]- 4.0,CartridgeOA[OD]- 4.0,CartridgeOA[LENGTH] – SeatingDepth – 4*PrimerOA[LENGTH]];

	//———-
	// Define shapes

	module Cartridge() {

	difference() {
	rotate_extrude()
	import("Cartridge – 20x102mm outline.svg",layer="Cartridge Aligned Half");
	up(PrimerOA[LENGTH])
	cyl(PrimerOA[LENGTH] + Protrusion,d=PrimerOA[OD],anchor=TOP);
	up(CartridgeOA[LENGTH] + CapsuleTip[LENGTH])
	cyl(SeatingDepth,d=Capsule[OD],anchor=TOP);
	up(CartridgeOA[LENGTH] – SeatingDepth)
	cyl(Void[LENGTH],d=CapsuleTip[OD],anchor=BOTTOM);
	if (Powder) {
	up(Void[LENGTH]/2)
	cyl(Void[LENGTH],d=CapsuleTip[OD],anchor=BOTTOM);
	up(2*PrimerOA[LENGTH])
	cyl(Void[LENGTH],d=Void[OD],rounding=Void[OD]/2,anchor=BOTTOM);
	down(Protrusion)
	cyl(Void[LENGTH],d=PrimerOA[ID],anchor=BOTTOM);
	}
	}

	}

	module Primer() {
	difference() {
	cyl(PrimerOA[LENGTH] – Protrusion,d=PrimerOA[OD] – HoleWindage,anchor=BOTTOM);
	up(PrimerOA[LENGTH])
	spheroid(d=PrimerOA[ID]);
	}
	}


	//———-
	// Build things

	if (Layout == "Show")
	//render()
	difference() {
	Cartridge();
	cuboid(3*CartridgeOA[LENGTH],anchor=LEFT+BACK);
	}

	if (Layout == "Build") {
	Cartridge();
	right(CartridgeOA[OD])
	Primer();
	}

view raw Cartridge 20x102mm.scad hosted with ❤ by GitHub

The New Hotness

3D Printed 20×102mm Cartridge