Terry beat me to it in a way; I didn't notice that this gentleman had a simple type of bore sight (before Terry mentioned it) in his guns muzzle, but I had intended to ask this question: Wouldn't the members with guns that have exaggerated muzzle swells (muzzle swells that were equal to, or greater than the diam. of the base ring) built into their design, have a distinct advantage over those whose guns had muzzle swells smaller than the diameter of the base ring? I hope nobody minds that I'm going to answer my own question here: You're darn tootin' they would! So, wouldn't it be more fair to allow the use of this kind of simple reference gauge, (I don't think this would really even be qualified to be called a sight) in order to level the playing field? Now, I'm not talking about anything that is aligned, (say by locating pin, or by some other means) but just a reference to duplicate the top of the muzzle, so the shooter has a fair way of judging elevation.