I have a winchester 1300 --carries either 12 of the buck or 11 of the slug rounds. I love them--I bought a case---its like shooting a 20gauge with good patterns at 15yards. Best inovation in shotguns in a long time.
On the Aguila website, they state they cycle fine in the 1300 Defender; but, Mossbergs and Remingtons need a "minor modification in their elevators to produce similar results."
Between 12 in the tube, one in the chamber and double-stacking them in the sidesaddle carrier, my 1300 can carry 23. Hope I never have to use them....