The ultramags are too large in diameter to fit and feed properly in a remington detatchable magazine.Even the magazine insert for the bdl models has holes cut in the side to provide more room in order to get three ultra mag rounds to fit.If the ultramags would work properly in the remington detatchable mag I would have them on all my rifles.As it is I have one 7mmstw converted to the detatchable mag system and it works very well.