In looking over nut samples from this year's nut evaluation, I noticed a particular pecan shell characteristic that seems to limit percent kernel. Its not what you might be thinking. Yes, shell thickness is obviously an important determinate of pecan shell-out percentage but the shape of the shell can also impact percent kernel. Take a look at three seedling pecans (photo below).
Even if a nut has a thin shell, the pecan that has the extended apex characteristic produces a lump of heavy and unproductive shell at its tip. Pecan cultivars that share this shell shape usually produce 44-48% kernel. Cultivars blessed with exceptionally thin shells and cursed with an extended apex will produce 50% kernel at best.
Other cultivars that share the extended apex trait include Goosepond, Colby, and Niblack.