Yes! They all behave differently inside the gun, so they all affect the ballistics. Specifically, the deformation properties affect the interior ballistics.

haha, no - not to any meaningful degree. Are you getting this from ChatGPT or something?

Jacketing is convenient for encapsulating lead, but you can run gas checked hard cast at generally the same velocities without any real issues. In that case the gas check is due to coppers higher melting/vaporization point. They are more expensive to make however, and finicky, which is why you don’t see it in production bullets.

The ‘copper’ pellet you mention was almost certainly not actually fully copper, but rather copper washed lead. But you can have lead harder than normal copper (heat treated hard cast is extremely hard and ductile), and copper softer than normal lead (annealed copper is extremely soft). Most copper people are used to working with is work hardened, but it’s trivial to make it ‘dead soft’.

That also has nothing to do with aluminum or other rounds you mentioned.

If anyone even uses them, which they don’t outside of very niche cases or experiments where it shows exactly what I am referring to.

density, however, is 99% of it. including for terminal, interior, and every other kind of ballistics. BC is king. And that is something that is impossible to fake, heat treat, work harden, etc. out of.

For example, initial engraving pressure can be changed or negated by minor changes in throat, regardless of anything else. Or a coating. Or any number of other things.

there is no replacement for dense mass.