Dragon's Doom Magic weapon

[KainPen]

I came accross this looking for a weapon I may want to buy for my hell knight later down the line.

Dragon's Doom is a +2 Dragon Bane Halberd, that glows when dragons are within 100ft away. 3 times per day it can also ingore dragons DR as a free action. Is this a mistake? As the weapon is already magic and can go through Dragons dr anyway? Does dragons require +x weapon again to go thru dr?

[Thazar]

You are correct that most dragons only have DR/Magic so it is a moot point. But I suppose that some future dragon... or a dragon with a template may have DR/Adamantine or DR/Good or something that this item could get through.

[KainPen]

yeah looks like it would only be useful vs alignment based dr and epic with mythic stuff. The weapon become +4 so it goes through adamantine also vs dragon. So it is very very redundant.