Originally Posted by szhttm
Anytime you see "+1" means that you would need to load one round into the chamber from one magazine, remove that magazine, and then insert a full magazine with the full amount of ammo it was designed for.
Sorta. Most manuals will specify how many rounds the mag will hold. The "+1" designation comes from the option to carry a chambered round. For example, "9+1" means nine rounds in the mag and one in the chamber. You load one round into the mag, chamber it, the drop the mag, and load the specified number of rounds.
The exception to this would be a Pearce +1 magazine extension which does, in fact, add one round to the magazine's stated capacity.
Many magazines can be tough to load to full capacity, especially when new. Get yourself an Uplula. It works miracles when trying to load a mag with stiff springs.