Interesting point. Although, a 5cm nail is tiny, that's like what you'd use to hang a picture on the wall. A real carpenter's nail is what I was picturing and

Interesting point. Although, a 5cm nail is tiny, that's like what you'd use to hang a picture on the wall. A real carpenter's nail is what I was picturing and that's more like 10-15cm which 2-3x's your impact depth (which is still only ~1km). So I think if anything, your point is basically proof that a nail or any traditional gauss gun projectile would absolutely ablate into gas immediately when fired at the hypersonic speed of orbital escape velocity.