With the caps removed you can now unscrewed you can now remove the gas storage tubes.

Start looking down the tubes you will see that the tube is divided into three section. You can take a set of medium sized needle nose pliers and sick them into two sections of the tube. Then using steady but firm force begin unscrewing them from the rest the magazine core.

If the tube came off when you went to remove the cap just use the pliers and the 6mm hex to remove cap.