Remove the gas system. Drift out the black cross pin out of the magazine tube. The pin is directly below the gas system through a polymer plug. The polymer plug should come out of the top of the magazine tube when you remove that pin, so be VERY careful when removing the pin. Now remove the magazine spring. On the follower end of the spring should be the plug you are wanting to remove. Remove it from the spring. And put the spring and polymer plug back in. The dished end of the polymer plug goes toward the end of the magazine tube.