Passengers inside an aeroplane, that is going through a free fall can feel the effect and if the fall is fast enough, they could even be levitated inside the plane. The same effect goes with a free falling elevator.

But passengers inside a bullet train feels no significant changes even though the speed of a bullet train is faster than that of a free-falling elevator.

Is there any explanation for this?

I have been taught that acceleration due to gravity is affected by surface area and not mass. I still find it hard to believe that a situation like in my question would be possible?

If a bullet is fired directly at the Earth at a velocity X and an identical bullet is dropped - assume they are spherical and there is no rifling in the gun, just to keep things even; is there an altitude Y from which they would hit the ground at the same velocity? (I know they will not hit at the same time). Or perhaps a range of altitudes?