Laughingdog ...

.
... sums it up nicely:

So in NY, it sounds like 7+1 is legal, since the magazine still only has 7 rounds. But if I accomplish that by putting 8 in the magazine and then chambering it, i'm a felon. But if I insert a 7 round magazine, chamber a round, remove the magazine and add one round back in...I'm perfectly legal.

Yep, about right!

pm