I have run Polycarbonate clear in the past but this one job we always fight black specks. Looking for ideas to solve.

We have pulled and cleaned screw and barrel, and on the very start it comes with a lot of black specks. Then it gradually has lets black specks, but, never being completely gone.

Barrel holds 8 - 9 shots (too many) Barrel temps are 520 in rear to 630 in front. (Has to be hot to get to fill out, but even at 630 front, I don't see any yellowing.)

Have tried slow screw RPM with low back psi. Screw and Barrel are new / general purpose. We can only run in this machine because of the PSI reqd.

Thx for any help,