The "or there may be a burr or nick in the barrel slot" < this is the problem! Some that I have seen haven't looked that bad but still caused the barrel to jam. Others that I have seen are so bad it looks like the slot was ploughed out making a high ridge along both outside edges the length of the slot. I am not sure how these barrels worked at all without jamming immediatly! As I stated before I can't get any pics right now because I don't own any of these engines myself and never will. I only brought the issue up to point out that to me, there are more user friendly motors available in the same price range. [8D]