I have put a few thousand rounds over that extension. Nothing has ever made contact. I do get a bit of carbon build up and just scrape it off at the end of the season.
With the CC tube (7 rnd) and the 3 round extension, I can feed 10 in the tube. When a stage permits, I can start with 12 in the gun: 10 down the tube, 1 in the chamber, and 1 ghost load.