Abstract Field-dependent AC susceptibility measurements are correlated with the transport critical current density ( J ct) and microstructure for some 20 Ag-clad (Bi, Pb) 2Sr 2Ca 2Cu 3O x (2223) tapes having J ct (0 T, 77 K) values ranging from 0–20 000 A/cm 2. Fields of 0.1-1 mT induced a double transition in the real component of the susceptibility of all samples. The field dependence of the lower temperature transition ( T' ( H)) exhibited a marked kink at 80 K and was always very sensitive to the applied field above 80 K, indicating an electromagnetically granular behavior. High-resolution transmission electron microscopy often revealed (Bi, Pb) 2Sr 2CaCu 2O x (2212 phase) intergrowths at the numerous (001) twist grain boundaries. Samples with a high J ct (0 T, 77 K) had only occasional half layers of 2212 at the (001) boundaries and required correspondingly higher fields to induce a kink in the T'( H) characteristic. The universal appearance of a kink at 80 K in all samples and the strong correlation of the field required to produce the kink to the zero-field, 77 K transport critical current density strongly suggests that c-axis transport across (001) twist boundaries within grain colonies controls the critical current density, even in relatively high J c BSCCO-2223 tapes.