Originally Posted by
Trenloe
See RS2.016 in the issue tracking thread linked in post #2.
The way FG does it is not in an improper way. From the Core Rules: "The GM might allow you to roll the dice twice and double the modifiers, bonuses, and penalties instead of doubling the entire result, but this usually works best for single-target attacks or spells at low levels when you have a small number of damage dice to roll."
From this, we see that "roll one set of dice and double the result" is purely a convenience when playing with real dice - the game can slow down if a player had to find a lot of dice (especially at higher levels they have be roll 6 or more d8s, for example). In FG we don’t have this restriction.