One reason is the Winchester hull. Several of the other loads use Federal hulls, which give lower pressures. In the case of load #8, which also uses an AA hull, Bell compares it to a load in a Federal hull. The Winchester load produces almost 2,000 psi higher pressure at the breech, with 2 1/2 grains less powder. You can get lower pressure reloads with Winchester hulls, but you have to be selective when it comes to your choices of powder, wad, and primer.