Like the post title says. Who else has DD'd their launcher? What are you doing with it? What are you shooting?

I've gotten my stamp back, and am working on 3D printing finned projectile prototypes. I have a stash of the ones made by Relodable Shells but I'm dissatisfied with them, because they're sub-caliber, sized for the inside of their 26.5mm shells, and the American Specialty Ammo shells.  They're works of art, made from whatever tough plastic they sourced, turned on a lathe, but they're just too small, only about 20mm, which doesn't hold squat, and 26.5mm is already challenged on the payload size as it is compared to 37 and 40mm...

So I'm working on a bore-width design, two parts, capsule, and fins,

And I'm working on designing a drag-stabilized hollow base Foster type 4ga/26.5mm lead slug as well. And trying to develop loads for it.  I'm hoping to do about 2oz at 950fps. inspection, measurments, and magnafluxing after some sandbags and a loooooong string.

Yesterday I worked up a prototype dummy 26.5mm smoke/flare capsule, with a stepped 20mm plug/base to fit in a American Specialty Ammo 26.5 reloadable casing.

The Sketchup design..



In the act of being printed. The thicker outer base is a disposable support to hold up the step or ledge, because the first layer or two of melted plastic coming out of the printer's extruder tip doesn't like hanging in thin air. I scaled the vertical axis down to 66% to save on print time.  It has solid cross bracing inside because it's just a dummy, and doesn't need to be hollow. Cameo appearances by "Mr. Bacon" drawn by one of my daughters, and the "Periodic Table of Meat" keeping the filament spool company.



Here's the final test projectile with the printing support skirt for the edge snapped off. An even shorter hollow based version of this will also be the prototype for the lead slug too.

I'm just using the free version. There's a plugin-for Sketchup that exports directly to a .STL file.  https://extensions.sketchup.com/en/content/sketchup-stl

I'm using Cura as my slicer in Repetier, and I do get "Manifold, not water-tight" warnings on some files, but if any flaws or gaps are within the layer thickness, the printer just keeps on chugging along.  I find there's a lot of false positives on this warning for many .STL files I'm trying to print, either tiny errors in the geometry that are way smaller than the print resolution/layers anyway, or it really is something you want to be hollow, but the slicer just doesn't get that it's okay.

Although, for the flare/smoke capsules, if I use tools like the offset, and stretch, or the "shell" plug-in from the Sketchup Extensions site, it comes out okay with no manifold/watertight errors. They're a lot easier than fiddling forever to make stuff join up. I was screwing around forever trying to draw a nosecone centered and parallel inside the outer nose cone to get my thickness... and then went searching knowing there had to be a better way, and found the "shell" plug-in, and had a perfect nosecone with thickness in about 20 seconds.

For instance, here's the underside view of making the nosecone/capsule body for smoke/flare. These are thicker than something that's going to be a chalk marker, so it doesn't burn through or melt right away, although I might work out some relief vents for them eventually for smoke... I'll see how it does squirting out the fuse channel in the fins first.

I start out making a line on the axis, using the arc tool with that line as endpoints, then stretch it out to half the diameter of the 26.5mm bore, or 13.25mm (Use the 3D printer template workspace, so you get fractional milimeters...) Then I draw a perpendicular line to the midpoint of the arc and erase the bottom half. On the same axis as the original line I drag out a circle, then use the "follow me" command so it sweeps the 1/2 arc into the nosecone shape. Then I drag out the bottom tube from the bottom circle of the nosecone. Then I group selected all the points of the nosecone, and used the "Shell" plug-in tool to make it 3mm thick to the inside.

Voila, a heavy nosecone.



Here's the video I followed to do what I described above, save for the shell plug-in to add the thickness.

Here's the finished prototype. However, it's on hold until American Specialty Ammo delivers my reusable/reloadable 26.5mm cases so I can get an exact micrometer measure of the inside diameter etc. Then I'll try for a finalized version.

Improvements I want to make are a version with a thin shell for chalk.  Spin/twist the fins a bit more, and add curved fillets between the fin roots and where the fins join the base to reduce drag a tad, and to add strength and more "meat" so I can add a properly dimensioned 3mm hole through the center of the fins for Visco fuse.

I wish I could tell you more, but I'm still learning as I go. And the one I've got, the Fabrikator Mini from Hobby King is the cheapest/smallest one I know of, so in 3D printer terms, its like a guy owning nothing but a tiny FIE Titan .25 ACP trying to give "gun advice".

My advice is buy what you can afford, what a lot of other people seem to be buying, and a lot of people aren't complaining about, and then just keep on searching google and putting it together as you go. The beauty of it is that so many people use the same printer control/server software like Repetier Host, and many of the same popular "slicers" (the secondary software that takes a 3D model and figures out the layers the print head will draw) that even if it's not the same printer, a lot of the technical information transfers no matter what you wind up with.