Actually, the diameter of 000, 00 & 0 buckshot varies quite a bit by maker (though within the same company it is very consistent in diameter) , so you may well have been using 0 buck.
That's why I told everyone on another thread to MEASURE several brands before you buy an 8-pound bag. - An 8-pound bag will keep you shooting small game for a LONG time, so measuring carefully is worth your time.
(It's also a good plan to test for "softness" by doing the fingernail test".)
yours, satx