On pages 22 and 23 of the IM, transitions with tube fed rifles are to be done with ammunition in the tube, the plunger locked, the flag in, and the safety on. Loading will begin when fully in the sitting or prone position. At that time the flag is removed, the safety taken off and a round chambered. With the flag in during the transition a round cannot be chambered. With mag fed rifles the mag may not be inserted before the loading process begins. There is nothing specifically said about not transitioning with ammunition in the rifle. That is simply a natural assumption when talking about mag fed rifles. It is best to refer to the IM instead of what someone else may say.