Bug: Stormcaller grants 2 additional attacks per round and the remaining 2-handed weapons (Purge, DS, BB, MM) do not grant any additional attacks per round.
Methods: I was checking out my warriors to ensure they all had melee perfection. While doing this, I found that my ASGW using the SC had 10 attacks per round and my ASGW using Purge only had 8. I then removed all items/armor off of my warriors - 3 are ASGW and 2 are AEGW. The two AEGW I kept BoCs on to decrease their encumbrance. All the warriors have melee perfection learned and level 7 in the weapon used. All the warriors have base dex of 7. The findings did not change in terms of the difference of number of attacks when the giants were naked vs fully armed. Here is what I found:
SC Warrior: Encumbrance 13%, 6 attacks/round when SC not equipped, 8 attacks/round when SC equipped
MM Warrior: Encumbrance 13%, 6 attacks/round when MM not equipped, 6 attacks/round when MM equipped
BB Warrior: Encumbrance 12%, 6 attacks/round with BB not equipped, 6 attacks/round when BB equipped
Purge Warrior: Encumbrance 11%, 6 attacks/round when Purge not equipped, 6 attacks/round when Purge equipped
DS Warrior: Encumbrance 13%, 6 attacks/round when DS not equipped, 6 attacks/round when DS equipped
Additionally, the SC Warrior has level 7 in both 2handed swords and mauls. I exchanged the Purge and SC on this character and it demonstrated the same findings: SC adds +2 attacks/round, Purge does not add any attacks per round.
Thank you and look forward to your response.