Doug, I saw that too in Quickload and wondered about it. It appears to me that F is Federal brass, N is Nosler brass, R is Remington brass, and W is Winchester brass. I don't know what the "@" symbol means. There is slightly different usable case capacity between each selection.
I recommend taking 3-5 brass with the primer in and weigh each one, then fill them to water to even with the top and weigh each one. Then average the 5 measurements (weight with water minus empty weight). Use this H2O capacity to make Quickload more accurate for the brass you have by typing in for "Grains H2O" the capacity you measured for your brass.