Duh-OH! Once again foiled by cheesy AD&D redefinition! What the heck is a sling bullet? a baby Bullette? No, I guess it is just a small ball used as a projectile, something a sub-atomic particle may not qualify as even if it is used as a projectile.
I don't think there are weapons capable of firing projectiles that capable of provoking nuclear fission or fusion, and you can't use a particle accelerator as a rifle or mount it on a tank, destroyer, gunship, bomber or fighter, and anyway, and as I already said, in the context of the phrase, I was referring to bullets as the ammo used on firearms. And also, if it is so important, then I'm made of quarks, and quarks are bulletproof
Finally, provoking fission or fusion while being at 100 ft. of distance from a target is suicide, so atoms are still bulletproof from your wider definition of what is a bullet applied to practical contexts.
