Remington 870 Mcs Price What Is A Super Mag Reciever On A Remington 870 Super Mag?

What is a super mag reciever on a remington 870 super mag? - remington 870 mcs price

I bought a Remington 870 Magnum and I'm super ready for goose hunting black cloud bought 3 and a half-inch balls, but the barrel of the gun that says I should like balls have a receptor super shoot 3 inch half and it is something that I should buy or already in my gun?