What really are Tech weapons?

We know that power weapons use regular ammo which bounces off surfaces, smart, which use homing rounds that automatically curve their trajectory to hit the target, and tech weapons which shoot electricity... Except they don't. You can't shoot electricity, it's impossible, and even if you won't deal any damage. The whole idea of Tech or Electromagnetic propelled weapons is to shoot projectiles extremely fast, like 6+ mach, which allows to penetrate really thick armor, walls and overall have extremely high energy. However I just can't figure out what does this ammo consists of, is it super hard bullet covered with special, super powerful propellant or is it just the bullet which is then propelled by the gun itself, and where is the energy for allat coming from? What do you think about it?