To increase robustness of dart use alternative materials for tip, shaft and cone:
3 mm Carbon fiber rod (tapered down to 1.5 mm by manual grinding)
Performance: Carbon fiber is extremely stiff so almost 100% of the motion energy of the dart will go into penetration of the target, rather than bending the shaft.
Alternativly one can use 5mm Bamboo skewers which are cheaper, but less stiff and straight.
1 layer of 0.1 mm Polyester (PET) Film ( Transparent foil from laser printer or copy machine)
While rolling the cone the film is glued together with super glue (4mm wide area.)
Performance: The cone is water proof, and can stand hundreds of shots to a rubber target
The cone prevents the dart from waggling at main shooting speed.
4 mm spring steel (pointed and glowed at the end to enable drilling 3 mm hole for the shaft)
Performance: When hunting outdoor and accidentally hitting a stone then the tip will not be destroyed.