I use 5" left wing helical base cut Parabolic shaped feathers. I just like the looks and that's what I learn to burn in the old days and when cut feathers came on the market I just switched to them. Burning really smelled up the place.
I don't know if they fly better because of the shape but I think, and correct me if Im wrong here (like I need to add that) don't parabolic have more surface area in comparison to feather of the same lenght but other shapes?

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