A multichannel wave screw with a slush channel barrier section adapted to provide a consistent mixture of 50% solids and 50% melt to both channels of the double wave metering section. The screw includes a barrier flight having a relatively large initial clearance which allows solids to enter the newly formed slush channel. The barrier flight gradually decreases in clearance to a final barrier flight clearance which allows some dispersed solids to enter the slush channel. At the terminal end of the barrier section, the barrier flight abruptly increases its pitch, thereby abruptly narrowing the solids channel and therefore forcing solid material over the barrier flight and into the slush channel. In this manner, a uniform mixture of solid and melt is provided to the multi-channel wave metering section.