Newton's (1st, 2nd, or 3rd - pick one) Law Of Motion states that any action has an equal and opposite reaction.What is the justification for the Gauss rifle having no recoil?
The recoil in a 'firearm' is from the explosion of gunpowder - also the cause of any sound except for the whizz of the bullet through the air. You're not just pushing the bullet down the barrel of a normal rifle, but the gas and particulates of the explosion as well. And that has more mass then the bullet, I believe.
There is no explosion in a Gauss weapon as far as I'm aware. It depends whether or not the EM coils in the gun 'pulls' the projectile or 'pushes' the projectile out of the end of the rifle. If it 'pulls' the projectile, then 'recoil' would tend to pull the gun out of the owner's hands. The recoil calculators are for 'firearms' and wouldn't have any bearing on a gun of this type, I would think, except for the rocket rounds. The difference in size of a Gauss needle and the gun itself would probably tend to lose any inertia whatsoever. You're talking maybe a .01 gram needle pushing against a 10 kilogram gun - negligible. And if you have, say, 10 coils that accelerate the needle, each coil is going to impart inertia singularly, as the needle passes each coil, not all 10 at once.
I would say that shooting a Gauss weapon would be smooth as silk. When you add in the rocket rounds is when you would start to get recoil.
Just my .02Cr
Dameon