8 shot mag tube for Mossberg 500?

[Gunman21]

I have a 20 inch barrel Mossberg 500 with a 7 shot mag tube. I noticed with seven shells (2 3/4) there is still 5 inches to the end of the mag tube. I was wondering if there is a different spring I could use to fit an extra shell in. I have also heard that the 590s hold 8 in the mag tube. Please someone clear this up for me. Thank you.

 

[dak0ta]

7 in the tube + 1 in the chamber = 8 for Moss 500
8 in the tube + 1 in the chamber = 9 for Moss 590

 

[MAKster]

The 590 models can hold one more shell in the tube because the mag cap goes on the outside of the tube. On the 500 the piece that attaches the barrel to the mag tube screws into the tube and takes up space.