How far would a Boom gun propel a Glitter Boy if the jetpack and anchors were disabled?

The Palladium Rifts Glitter Boy Boom gun accelerates a flechette round of ammo at over Mach One. Normally, laser tipped anchors from the legs drill into the ground and a jetpack provides counter thrust to offset the recoil.

If both of these safety mechanisms were disabled, how far would the gun propel the Glitter Boy power armor in earth normal gravity at one atmosphere pressure?

A player wants to use a prepared action to "offensively dodge" an anticipated enemy action.