I supervised an Honours Thesis on the topic of using a long coil gun in an inclined mine shaft to launch small payloads into Low Earth Orbit. Nick has nailed it: The G forces are too big for people. Simply launching small bits of hardware requires heroic effort. A big gottcha is muzzle velocity. The projectile needs to have orbital velocity at almost zero altitude. The tunnel of the coil gun would be pumped down to a hard vacuum otherwise the bow shock from the projectile would toast the magnetic coils in the tunnel. A diaphram is placed at the muzzle end of the tunnel between the tunnel's hard vacuum and the ambient atmosphere. The projectile pierces the diaphram and in a millisecond goes from zero atmospheric drag to zillions of tons of atmospheric drag. That deceleration alone would crush a human cargo into protoplasmic jelly. The concept seems cool when you read it in Jules Verne's novel but the hard engineering practicality doesn't work out.

Gary