Another difference I noticed is the barrel bushing, and how the recoil spring was contained on the -2. My 39 had the recoil spring retained by the barrel bushing like with a 1911. Unfortunately, the bushing flexed, causing grab marks on the aluminum recoil spring guide. The grab marks wore through the anodizing to the bare aluminum underneath in short order,The -2s had the recoil spring captured by the slide itself, and the bushing became open on the bottom as it no longer contained the recoil spring. And no more grab marks on the recoil spring guide. Having the slide itself retain the recoil spring allowed the fixed barrel bushing seen on S&W auto pistols that followed. A definite product improvement IMHO.