Regarding the SO guns, as OWD stated, the "S" stands for Sovrapposto, which translates to superimposed or superposed. The "O" is just used for nomenclature and does not represent a formal word. The numbers after SO refer to different gun configurations (target and field) over the eras (Beretta began making O/U guns in the 1600's and SO model guns in 1932). Both ASE and SO guns were/are made in Beretta's Due factory, which produces their premium-grade guns. EL and EELL models have more bling (i.e., "extra luxury") and put a bigger dent in your credit card.