Err, unless I am grievously misinformed, neither the M1A1 nor the T-80, nor any main battle tank, uses recoilless rifles as a main armament. A recoilless rifle is not far removed from an RPG, with the main difference really being the round fired, rather than the "gun" itself.
Hence, any railgun will have a dramatically higher recoil than a recoilless rifle firing the same round at the same velocity.
Also, the main thing that causes recoil in a conventional gun is most definately the force of the exploding gas pushing back against the gun. The friction between round and barrel would actually work to reduce recoil, since the round would want to drag the gun in the opposite direction of the recoil.
To clarify, it doesn't matter how you launch the shell, whether it's through a railgun, a conventional cannon, or a rocket motor, there is always exactly the same amount of recoil. The only difference is what absorbs that recoil. In the case of a rocket, the recoil is felt by the air, or anyone standing directly behind the motor. Otherwise, it's absorbed by the gun itself.