The magazine allows you to pull the collar down as you drop the ammunition into the magazine.This makes it possible to drop several rounds in at a time and load magazines in a fraction of the time with far less effort.The speedmag works in all mil-spec ar-15 lower receivers and will accept any ammunition that fits in regular mil-spec magazines like.223 remington, 5.56 nato, and.300 aac blackout.Capacity: 30rdModel: SpeedmagCapacity: 30