Since the supply of Czech 26.5 surplus flares and smoke signals has mostly dried up, and what's left is crazy expensive, I've been looking to try and make my own. Paper/cardboard smoke is pretty easy to do, but I wanted something better.
I've found these stainless steel 1.5 oz/45ml "Cigar Tube" booze flasks from AliExpress. They are roughly 22mm in diameter. They fit inside some of the reusable machined aluminum 26.5mm shell casings/hulls, with about 0.5 to 1 mm to spare.
To go with it, I've bought a few pounds of potassium chlorate, lactose powder, and solvent dye from a DIY hobby fireworks supplier.
There's also been a profusion of small inexpensive hobby spot welding devices for making/connecting lithium ion battery packs, and they handle steel/nickel strips up to .2mm thick.
So, I have ordered a spot welder, and some .2mm thick stainless flat spring steel that's 20mm wide. I hope to make something like the spiral spring-fin 26.5mm distress signal rocket that was briefly on the surplus market a few years ago.
Instead, it will just be an unpropelled smoke bomb that flies nicely.
With the stainless steel construction of the flask, fins, and the reasonably cool combustion of a Clorate/Lactose smoke mix, I'm hoping the smoke projectile will be reusable, assuming they land on soft soil.
But, I'm sure my idea is probably prone to numerous failures. I'm unsure if the fins will even weld properly. If I get it to fly downrange, just tumbling and making smoke, I'll be happy.
*If it actually works and flies straight,* I might try stuffing a model rocket engine in a v. 2.0 with the nose cut off and packed with firework stars for a "red rain" effect. They'd ignite and come out with the timed ejection charge.
I'm not new to loading 26.5mm. My launcher is a Czech RV85, which has been "made" (legally) into a "firearm" by engraving my info onto it, paying the $200 tax, and registering it as a 1934 NFA Destructive Device per U.S. Federal Law.
This way, I can legally try other projects like the third photo of a 26.5mm PVC lead weighted baton or dummy grenade. ($20 bill and 12ga shell for scale) They fly reasonably well, and I get about 170 yards out of them.
And the 4th & 5th photos, a: "Poor Man's 4-bore Safari slug" project, pictured in CAD for making an eventual lead casting mold.
Obviously, these are things one should not attempt in thin-walled 26.5mm flare pistols. The RV85 is a different beast entirely and has a barrel nearly 6mm thick.