[SampleMan]

If you do the math, a rail gun would have to be well over 10 miles long to accelerate a vehicle to the required speed without exceeding 7 G's. The angle is going to have to be high if you are going to go "up", and it can't have much bend or lateral acceleration in the last few miles to prevent the same. This would lead to a very deep below ground requirement. Depth not distance being the problem for digging such a tunnel. We're talking much deeper than South African diamond mines.

Why would you want to do that, so that you could start from sea level?

[The Red Zone]

Chewing down the middle of an equatorial mountain would require the same thing.