You may want to elaborate a bit. I can think of three different Remington Rangemasters off the top of my head, and the only one I can think of that had a detachable magazine was the Model 37, which was a .22LR. The others, are single shot (XR-100) or have an internal magazine (40-XB). I think there was a M700 Rangemaster as well, but I am pretty sure that was a 5 round internal as well.
What model is it?