Sometimes the rear barrel band is stuck to the barrel; try some penetrating oil, like Kroil, at the top of the barrel/band then tap the band with a rubber mallet or soft wood to get it off. Other times you have to remove the front sight, the front barrel band, the rear barrel band, and the magazine tube before you can get the forend off. Just depends on the angle between the barrel and the magazine tube on how much pressure is being put on the forestock and wedging it in.
