I am not, nor do I claim to be a bullet expert in anyway, shape or form. Bullet science requires the design, weight, material and more to truly ID who made a bullet. I am going to be very general in my description of bullets and focus on the main type of bullets you may encounter. Many more exist than what I am displaying. Many companies also had their own design slightly different to distinguish there work. Keep in mind this is very, very general.
Bullet material:
Many bullets are made now of Wood,
plastic, Steel,
Copper or Nickel jacketed Lead, Lead-Antimony alloy etc., and a shift to green
ammunition made of solid Copper, Brass, Bronze, Zinc, Plastics, Nylon, Rubber and
more are being more common. Bullets have also been coated in Teflon (but this is
now illegal in most places), molybdenum, Boron, Boron Nitride, Tungsten,
Tungsten Disulfide, polyester, Polyurethane, Cerakote (ceramic) and many other
experimental coatings and new design.
For the military, bullets have been made for grenade launching, dummy and training use, tracers, armor piercing, semi armor piercing, exploding, pepper infused, ink infused, multi ball, multi bullet, flechette arrows and for many reasons, whether experimental or for reasons not fully understood. Bullet type and design is an entirely complex subject of itself.