I don't want to post in SH's new thread but from my experience with 315 and similar systems, it is best to use only 25% of margin in trades instead of 50%. 33% is workable but 25% is safer in the long run. Sometimes I've seen trades quadruple in value from the span margin value and then for 1 or 2 trades, the span margin gets wiped out. Make sure when you open a trade, no more then 25% of margin is used. 50% is too little for a system similar to 315.
Hope that helps newcomers and even veterans who have yet to achieve long term success.