On the 15" ga line at the NW Penna Steam Engine & Old Equip Assn (Portersville Steam Show), we used 16 lb rail, it has held up MUCH better, and has less trouble with sun kinks than the 13 lb that we replaced. Check with a mining supply company or even a local model engineering/live steamers club. If I remember correctly, the last batch of rail and spikes at Portersville was actually donated by a local mining firm.