Not much help with the rails...sorry But, for the 540 you will need longer flight time to complete the extra 180 degrees of rotation. Some prewinding will help and making a quick edge change at takeoff adds a lot of energy to your spin....example, as you prepare to spin a BS 5, ride up the ramp flat based, then come in with a slight amount of heel edge to begin to slowly turn heelside. Just before the takeoff from a decent wedge, instead of ollieing off, make a quick, snap edge change toward your toe side, this, combined with an element of prewinding will really whip you around as you become airborne.
To do a decent 5, you be on a large enough feature with a steep enough ramp that doing an ollie is completely un neccessary, so increase spin rate, not height by timing this edge change at takeoff. It take some practice to get this timing diled in right, but then again everything in snowboarding does. I have not completely mastered this technique yet myself, but when I get the timing right, the rotation becomes much easier. When doing a 5, just remember that you need more air time to complete the spin so you have to go a bit bigger than what you hit for a 3.
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