An issue with PE barrel prior to the shaft 4 is the badge that sticks out. Try screwing your sl barrel again and see if the PE badge is obstructing you from screwing in the rest of the barrel. I know I had the same issue with my PE barrel and my shocker and autococker. Even the jewel on my lucky15 rubs on the body and front block on my free flow autococker.
I don't usually drink beer but when I do I save twice as much to go paintballing and then drink a beer when I get home