This extremely accurate 12" Cocker barrel is made of PPS special .685 smooth bore brass. The inside is polished to a mirror image to reduce friction on the ball. The dual spiral venting dissipates that blast behind the ball creating a less turbulent cylinder of gas. This helps keep the ball on course and reduces the report. . Each barrel includes a .685 Sizer and a .680 Sizer. Just slide in the sizer that best match the paintballs you are using.