No. A falling object is at "0G", it is "weightless" (in a "drop seat" type carnival ride, when the ride triggers, you have no force on your butt). A bullet is a falling object after it leaves the gun. You cannot measure earth's gravitational attraction from the bullet's frame of reference because it is 0. Therefore, you cannot use earth's gravitational attraction to measure the bullet's spin rate because the value is zero, and zero has no direction information.