3 1/2” models
3” and 3 1/2” magnum shells:  three in magazine, one in chamber.
2 3/4” shells:  four in magazine, one in chamber.

3” models
3” magnum shells:  three in magazine, one in chamber.
2 3/4” shells:  four in magazine, one in chamber.

3” and 3 1/2” models with three shot adapter installed
Two shells in magazine and one in chamber, for all shell lengths (2 3/4”, 3” and 3 1/2”).

Important:  because 3” and 3 1/2” shotguns can handle mixed shells of different lengths, total capacity may be affected.