Don’t remember if I saw it in the Ebay V11R thread or somewhere else but, someone mentioned it was possible but you had better be bullseye precise at boring the tube otherwise you risk making hole in your tube. Someone accomplished it but ended up wearing a hole in the side of the tube. Someone also mentioned something about a Solarforce or Surefire 18650 tube working. I can’t confirm that though. If that is true they might make a 18350 tube as well. Again, not positive on that.