Browning 2000 plug question

[JandSCattleCo]

Buddy of mine has a browning 2000 12 ga chambered for 3" magnums according to the barrel. It holds 4 shells right now. Looked online and it shows the plug as a metal piece with ridges on it. This piece is in his gun but again it still holds 4?

What does he need to do?

 

[Biggun4214]

Cut an old arrow or a 3/8 wooden dowel longer than the factory plug and put it in the tube.