I have been wishing for the same thing for my Badger bottom metal in McMillan A5. Have not had any luck locating anything. My Templar does not work for a hinged style bottom metal like Williams or BO M4.
I think a 3 round that fit flush, or close to flush, would be nice for a hunting rifle.
Is the bottom plate welded on the AICS mags, or does it slide off for cleaning like a lot of mags do?