We strive to cut the spru to the boolit base square yet we add a gas check that has a radius to its base - a function of "cannot get a square base from" the GC punch. Perhaps in the "heat of the moment" as the gas checked boolit is "spanked" by the high pressure spike and heated, it conforms to the inertia of the boolit and obturates to the side walls taking the shape of the chamber, rifling lands, and grooves. IDK...subtle maybe, and part of the "infinite mathematics" of the unknown Universe.
BOOLIT BASE
GAS CHECK BASE