After a request from my youtube viewer, I designed these 37mm projectiles. Then I discovered that 3D printed projectiles are already available on Thingiverse and ebay.
However, I believe my design still has some advantages.
1. Higher payload capacity than fin stabilized projectiles.
2. Better gas seal than fin stabilized projectiles. Many fin stabilized projectiles use a thin blast disk to push on the projectile. My design has a fairly thick tight fitting with a gas ring to further improve sealing.
3. Screwed on bottom is better than fricting fitted ones as seen on some designes on Thingiverse. They will not come loose. Especially after applying epoxy to the threads.
4. Boat tail design is better for aerodynamic in theory.
The file is live on LBRY. It contains 50mm and 90mm shells that corresponding to 3 and 4.5 inch long casing from exotic firearms. There are vented and closed versions for each length of shells for smoke and flair. The flat base plate is for casing with built in powder busing while the base plate with internal powder bushing is for older casings. There are two versions for the screw on end cap, too. The hand tighten only version has no wrench cutout so it will be the best for aerodynamic. But you may need to glue the thread. Another version has flat cutout so you can tighten it with a wrence. But the cutout may negtively impact aero dynamic.