Launching Ramp 2

so whats been the draw back to that mag lev concept? why havent the ruskies , chinese, french, israelieslooked at that option? Cryogenics was one problem before... what now? I'm open to anything :-) I'm trying to remember how to figure a constant acceleration curve that doesnt bust 3-4 g's max and still get the end point to escape velocity. Rockets do have one advantage since as atmosphere is reduced they can increase velocity, where as with this launcher "muzzle velocity" will have to be enought to surpass 17,000 mph AFTER plowing through all the atmosphere, even if launched at 12,000 ft altitude mountain as far as a remake of "When Worlds Collide" launch ramp, the mountain we got is the highest thing around, no other highpoint nearby to use a parabolic sled ramp :-(