User blog comment:Rozh/Surface-to-Orbit Artillery/@comment-131756-20110321005343/@comment-663564-20110321214741

The force would be massive, exactly equivalent to the impact force of the projectile due to Newton's Third Law.

The difference is that hitting a planet with a MAC projectile is dispersing that force in a very small area. This is how body armor tends to work: By dispersing the force of the bullet over a larger area. That is what you would have to do when firing a ground-based MAC, aside from other recoil dampeners.

"But the force is being produced by magnetics, so why would they produce recoil?"

- Tuckerscreator

Yes. The magnets are pulling and pushing the projectile, and they themselves are being pushed and pulled towards the projectile with an equal force. However, since they do not move, the force is dispersed down the barrel, which is why you would get recoil. Again: Newton's Third Law.