Sundering

what does it mean and what does it do for my sword?

guildwiki is your friend.

http://gw.gamewikis.org/wiki/Weapon_upgrade

In short, absolutely nothing. Vampiric is your true friend.

Armor penetration. 20% chance of 20% armor penetration.

Description: Sounds really good
Reality: It's sucks.

Vamp or Zealous.

Sundering gets better as your attack damage gets higher. Some use the mod as a swap when they are about to use a high-damage spike skill, since the extra 3-5 damage from vamp would be a drop in the water but a 1-in-5 chance at an extra 20-30 damage would potentially mean quite a bit.

Hah! Agreed. Vamp FTW

Originally Posted by Fender
posted this in another thread, but it is probably worth repeating here, with a little more information.

Against an AL 60 target w/ perfect vamp your damage increases over base by:
sword 8.8%
axe 8.4%
hammer 9.7%
bow 12.4%

Against an AL 60 target w/ perfect 20/20 sundering your damage increases over base by 4.6% for all weapons. Much better than the 1.1% a 10/10 sundering mod would get, but still well below vamp.

vamp vs AL 70
sword 10.4%
axe 10.0%
hammer 11.6%
bow 14.7%

sundering 20/20 vs AL 70 compared to base all weapons 6.4% (10/10 = 1.3%)

vamp vs AL 100
sword 17.6%
axe 16.9%
hammer 19.4%
bow 24.8%

sundering 20/20 vs AL 100 compared to base all weapons 8.3% (10/10 = 1.9%)

So, sundering still sucks, just not as much.

Wouldn't it be more like 10-15 damage? How much damage do your spikes do without the sundering bonus?

Use in a spike? How? Just what are you spiking with?
+dmg from attack skills is armour ignoring (calculated after armour) so Sundering isn't helping you except on the part of the damage that comes directly from the weapon (ie. its helping you no more than it would on a normal blow). Vampiric is far far far far far better (i cannot emphasize this enough).

Have you ever used sundering on a hammer muhahahahaaaaaa

iressitable max on 60al 122 with sundering max 153 with vamp max 127

http://gw.gamewikis.org/wiki/Damage

Read it, learn it, live it.
Sundering decreases your enemies AL, and so multiplies your damage, however +dmg from skills comes in *after* this step and as such is not multiplied by the armour step. Sundering will not make an attack skill increase in damage more than it would make an ordinary attack.

The particular salient point is:
ED = [([RD × DScale× AE ] + DShift) × DMult] + DNeg

your sundering will increase the value of AE, and thus your damage is multiplied up, however AE does not multiply DShift (which includes the +xx damage from attack skills).

The main disadvantage of sundering is that it's unpredictable. You never know when it's going to kick in. So it's you're spiking, you can't really depend on chance to make your spike work. Vamp on the other hand, gives a constant +5 damage, which can be depended upon.