The SASS rules state that the shotgun shall be staged "open and empty". The rounds are loaded on the clock. The rule was just changed at the last Territorial Governor's Meeting to allow loading two rounds in the magazine, if the bolt is closed on an empty round after firing a shot, again "on the clock". It's always been legal to load one in the chamber and one in the magazine.
I've tried loading both ways, singly and loading the chamber and then one in the magazine. I can load and shoot almost twice as fast by loading singly. The only time I load a second round in the magazine is if there is a clay bird thrown on report, or a "popper", which throws a bird a short distance in the air when the steel shotgun target falls.
So in answer to the original question, they're loaded singly due to a rule that required an empty chamber and the time involved in loading the magazine. There is a SASS match that does allow for a full magazine called "The Wild Bunch", after the movie of the same name. It also allows the use of a 1911, '03 Springfield and Model 12 shotgun. In our matches, the single action shooters generally beat the Wild Bunch shooters in time and hits. Don't ask me why, it just turns out that way.
Before anyone chimes in that this is poor training, SASS shooting is a game, and not intended as training, per se. The side benefit of the game is that any shooting you do is good training, the same as trap or skeet.
Hope this helps.
Fred
