The weights of flat bottom rail used in typical prototype 2′ narrow gauge railways ranged from 20lb-30lb (per yard) for small industrial use up to 60lb for ‘main’ lines. Nowadays some of the modern restored railways use even larger weights. Flat bottomed rail of these lower weights typically have square dimensions, in that the height of the rail matches the width of the rail foot, whereas the larger rail sizes such as used on modern standard gauge railways tend to be taller than the foot width.
Most model rail is a representation of a mainline rail size in a smaller scale so when used as narrow gauge rail in our scale it will either be too tall or too narrow. Usually the head width is noticeably too narrow as well.
The attached Rail Comparison Diagram (PDF) shows various model rail sections compared with typical prototype sections. More details are provided in this attached table of Prototype and model rail dimensions (PDF). Both include the dimensions of the rail sections from Karlgarin Models specially designed for 7mm narrow gauge.