It may not be as tough to clean as you think. There is a company doing Remington 700 conversions that uses cut off 6mm cases for ignition. The idea being that you don't have to clean much behind the breech plug. I like muzzleloaders because I can tinker with them and they force me to be patient. I like ARs because there's something cool about going through 90 rounds of rifle ammo on one stage of competition. I'm not sure I could get behind a single shot AR though.