How the game works out damage
A stat such as entity damage starts from a base value and a multiplier of 100%. The round sets the base (7.62mm Ammo: 47), the weapon adds its own offset and its quality bonus, then every mod, attribute, perk and book adds its percentage to the multiplier. The damage is base × multiplier, so two +50% bonuses make +100%, not +125%. Each installed mod also adds the weapon's mod power bonus of +10% to entity and block damage, whatever the mod does.
The hit is cut to a whole number. Past the falloff range the damage drops with the square of the distance and reaches nothing at the weapon's maximum range. A headshot adds the rifles' head bonus, then multiplies by the headshot modifier (+100% for every player, up to +100% more from the weapon's attribute) and by two: a Hunting Rifle that hits the body for 68 hits the head for 472. The sandbox settings for player damage and for damage entities take scale the result last.
Fire rate is the rounds per minute stat; the double barrel fires again a quarter of a second after the trigger is released. Reload time is the length of the weapon's reload animation divided by its reload speed, which perks raise. Sustained DPS counts the time to empty the magazine plus one reload.
Not counted: the random roll each crafted or looted weapon gets, armor set bonuses, the target's armor and its body part damage resistances, critical hits, bleeding, fire and other damage over time.