Abstract: A multichannel wave plasticating screw having a feed section, barrier melting section, and metering section wherein solid material is transitioned from the trailing side of the primary flight to the push side of the primary flight at the terminal end of the barrier melting section. The solids transition is accomplished by interchanging, or "reversing" the diameter and width of the primary and secondary flights at the terminal end of the transition section. Alternatively, the barrier flight includes a short section of increased pitch at the terminal end of the barrier melt section which abruptly narrows the solids channel and thereby forces solid material over the barrier flight into the melt channel and on the pushing side of the primary flight. Transferring solid material from the trailing side to the push side of the primary flight increases the shear and pressure applied thereto and more quickly and efficiently melts solids.