setting file is located in ems/bfggl/Settings.cfg in your main l4d2 directory

Disallowed_Gamemodes = ["rocketdude"] //which gamemodes the grenade launcher wont be a bfg
BallSpeed = 16 //the bfg ball speed in arbitrary units, no clue what they mean
BFGExplSize = 512 //the size of the bfg ball explosion
BFGExplDMG = 800 //the base damage of the bfg ball explosion (has falloff)
BFGSurvivorDamage = 300 //the damage the bfg ball does on direct contact with a survivor
LaserCommonDamage = 6 //the damage the bfg lasers do to common infected every 0.034 seconds
LaserSpecialDamage = 12 //the damage the bfg lasers do to special infected every 0.034 seconds
LaserWitchDamage = 8 //the damage the bfg lasers do to witches every 0.034 seconds
BFGAmmo = 2 //the reserve ammo the grenade launcher has