OK, so we have several magical weapons, instances and such that allow someone to cause 'double damage', whether it be someone swinging a backstab, setting a spear to receive a charge, and so on..

SO how do YOU Do it?

Is it just double the damage period (inc all bonuses from specialization, strength etc)?

Double the weapon, THEN add in bonuses?

Roll double the weapon, then add in bonuses??

Let's take a few examples.

Player 1 is a thief who lucked out and has a 16 strength. He's wielding a +2 short sword and is 5th level so is x3 damage for his backstabs..

So is that [d6 (sword) +2 (Sword) x3 (backstab multiplier)[, +1 from str? Giving him a damage range of 10-25?

Is that d6+3 x3, giving him a damage range of 12- 33hp?

Is it just 3d6, +2 magic +1 str giving him a damage spread of 6-21hp?

Or is it 3d6+6 (Sword x3) +1 from str giving him a damage range of 10 to 25hp?

Where as we then have player 2, a fighter who has 18/77 strength (+4 damage), is double specialized in the bastard sword (+3 damage), and is wielding a +3 bastard sword. The DM is using a "Nat 20 is double damage" rule..

Is that 2d4 (two handed S/M damage value) x2 + 4 str, +3 spec +3 magic giving him a 14 to 26hp spread

Is it [2d4+3 (sword) x2], +4 str +3 spec, giving him a damage spread of 17 to 29hp

Is it [4d4 (sword x2) +4 str, +3 magic, +3 spec giving him a spread of 14 to 26hp

Or is it [4d4+6 (sword x2) +4 str +3 spec, giving him a spread of 17hp to 29hp?

Or is it 2d4+10 x2 giving him a damage spread of 24hp to 36hp??

Does it depend on WHICH source the damage multiplication is coming from??

Linked to this IF say you are one of those who does double damage on a nat 20, and someone's already getting a x2 damage attack (Charge/set for charge), does it double again to x4? Or is it just X3?