With the mention of case stretching, less firings and/or extraction problems, what is less ideal? BA's having less of an issue with extractions than AR's without poor designs in what causes BA extractions, is it more about the groove? Rebated rims in AR's are less ideal, but some manage to have less problems? Is it case taper, shoulder angle or something else? With 22N and 284win (or other similar cartridges) rebated rims in AR's are they less popular because of not extracting or a grander scale? Someone had mentioned they have a 223wssm in an AR15, so there's possibilities for unconventional cartridges for many other AR platforms. So, what out of the norm cartridges do you have in an AR that function very well or some you wish you didn't have? Also, what about better and no so well designed cases for any type of rifle (semi, pump or ba)?