I've just picked up a fin that feels to have an unusually sharp leading edge. Checked all the old favourites, they're all different, but they all do appear blunter. ( Only going by feel, is there a way to easily measure small radii of curvature?)
Bethwaite in his book High Performance Sailing recommends 0.4 % of chord, that's a radius of 0.4 mm for a 100 mm chord. Maybe it's not as critical a parameter as Bethwaite suggests?

Now thinking about the manufacture, whether moulded or machined, the leading edge is going to be the hardest bit to produce accurately. It's where the mould splits, or it's the meeting point as the job is flipped while machining. So I suspect the leading edge is generally cleaned up in the factory by hand with a piece of sandpaper? In which case if the guy in the factory got distracted we should easily be able to finish the job ourselves. Any suggestions from the fin experts on how to go about hand finishing the leading edge?