OK so here is a simple breakdown of how ib works. Weapon dmg and light lvl are seperate stats not like pve. Lvl 32 with a maxed gun will dish out same dmg as lvl 31 with same gun, however the 32 can take more dmg. The dmg stat on ur gun alone determines dmg output. Light lvl/ Defense stat determines how many bullets you can take. Don't forget to turn bounties in daily or you won't be able to pick them up next day. Also the buff will increase xp gain by 10% as will the IB emblem, shader, and class item. Nightfall boost is also applicable. Here's this: http://planetdestiny.com/iron-banner-reforge-guide/