Today I recorded the number of "clicks" (notches past that required for a flush rivet) required to nest various thicknesses of sheet dimpled with various die sets. This list should be adequate to countersink the main longerons.
#3 Rivet Only 0
0.025 Standard 4 0.025 Tank 7 0.025 Sub Struc. 11 0.032 Standard 7 0.032 Tank 11 0.032 Sub Struc. 14 0.040 Standard 11 0.040 Tank 14