Bifunctional diterpene cyclase that catalyzes the successive two-step type-B (protonation-initiated cyclization) and type-A (ionization-initiated cyclization) reactions of geranylgeranyl diphosphate (GGDP) producing successively (+)-copalyl diphosphate and miltiradiene. (+)-copalyl diphosphate = diphosphate + miltiradiene (2E,6E,10E)-geranylgeranyl diphosphate = (+)-copalyl diphosphate Binds 3 Mg(2+) ions per subunit. Secondary metabolite biosynthesis; terpenoid biosynthesis. The Asp-Xaa-Asp-Asp (DXDD) and Asp-Asp-Xaa-Xaa-Asp/Glu (DDXXD/E) motifs are important for the catalytic activities, presumably through binding to Mg(2+). S.moellendorffii contains two distinct types of functional terpene synthases (TPS) genes, the typical seed plants TPS genes (SmTPSs) and the microbial type TPS genes (SmMTPSLs). Belongs to the terpene synthase family.