I don't really understand "upgrading" a gun... I had Xma13 gun for 4 years, but it never became rusty, but you can repair it in repair shop.

The Era Go item database mentioned that the gun can be upgraded "The XMA 13 deals 7 damage with a clip size of 15. The XMA13 Gun costs $7500 and can be found at an unknown location. It can also be upgraded at the Gun Repair Shop shop." Item Damage: 6.

So I'm guessing the description is wrong? Or I'm being stupid here. By the way, the gun only has 6 damage and 13 clips for me instead of 7 damage and 15 clip size... Am I doing something wrong???