Oh! Got another one:
Old School: Fixed choke barrels. One barrel, one choke, unless you want to stick one of those hideous polychokes on it...
New School: Screw-in chokes! 1 barrel, chokes from wfo to too-dang-tight! Need rifling, use a rifled choke! Got an older gun that you wish had a looser choke? You can possibly have the barrel reworked for screw-in chokes and the world is your oyster! Do they make a choke for keyboards? Mine keeps letting out too many exclamation points!
gp911