Why Does This Script for Bouncing a Bullet Off the Wall Completely Fail?

As the title implies, my game involves shooting bullets that bounce off of walls. Below is an excerpt from the script that is supposed to make it bounce; it is the code that runs once the bullet hits a wall. But when the bullet reaches the wall, it doesn't bounce; the Speed (the name of a BodyVelocity within the bullet that powers its movement) is deleted, causing the bullet to fall down and through the world. Why in the world is this?

            script.Parent.Speed.Velocity = Vector3.new(0, 0, 0) --Stop the bullet from traveling any further.
            if script.Touched.Horizontal.Value == true then --Calculating the angle that the bullet traveled at so that it can bounce off the wall at the same angle.
                c = {a.X, b.Z}
            else
                c = {b.X, a.Z}
            end
            disA = math.sqrt(((c[1]-a.X)^2)+((c[2]-a.Z)^2))
            disB = math.sqrt(((c[1]-b.X)^2)+((c[2]-b.Z)^2))
            theta = math.atan(disB/disA) --This math isn't really important, don't worry... Just think of theta as the angle that has been calculated (in radians).
            newDirection = Instance.new("Part", game.Workspace) --Making a new part that holds the direction that the bullet is supposed to face after bouncing off.
            newDirection.Name = "Vector"
            newDirection.Size = Vector3.new(.75, .75, .75)
            newDirection.Anchored = true
            newDirection.CanCollide = false
            newDirection.Position = Vector3.new(script.Parent.Position.X, script.Parent.Position.Y + 5, script.Parent.Position.Z) --Placing it 5 studs above the actual bullet.
            newDirection.Transparency = 1
            newDirection.Rotation = script.Parent.Rotation --Setting the rotation of the part to be the same as the bullet so that it can be rotated further with theta.
            if script.Touched.Horizontal.Value == true then
                if a.X < b.X then
                    newDirection.CFrame = newDirection.CFrame*CFrame.fromEulerAnglesXYZ(0, theta, 0)
                else
                    newDirection.CFrame = newDirection.CFrame*CFrame.fromEulerAnglesXYZ(0, -theta, 0) --Depending on the direction that the bullet hit the wall in, it'll bounce off in that direction.
                end
            else
                if a.Y < b.Y then
                    newDirection.CFrame = newDirection.CFrame*CFrame.fromEulerAnglesXYZ(0, theta, 0)
                elseif a.Y > b.Y then
                    newDirection.CFrame = newDirection.CFrame*CFrame.fromEulerAnglesXYZ(0, -theta, 0)
                end
            end
            wait()          
            script.Parent.Speed.Velocity = 20*(newDirection.CFrame.lookVector.Unit) --This is the part that messes up. When I run the script, the Speed (a bodyvelocity) is just deleted and the bullet falls through the world and is deleted. I have no idea why.
            script.Origin.Value = b --Setting a new A in the event that the bullet bounces off another wall.
            newDirection:Destroy()
        end
    end
--Please don't go off saying that I put in too many ends; I said in the premise of this question that this is an excerpt. The entire script is not shown. I know for certain that the amount of ends is proportionate to the if statements.