Soulbound Issue
Did you put a rune or upgrade on it? unfortunately that will soulbind the item – which I think is a really silly mechanic but anyway,
There is a workaround although it will take same gems.
Transmute the look of the helm onto a blue item. (make sure it is high enough to accept the rune if you put one on the helm). It will now be account bound. Transfer the helm to the character you want to have wear it and then use a trans splitter and it will now be soulbound to the new character.
Kind of a lousy way to have to do it and considering the number of people that wind up accidentally soulbinding items you would think a reasonable company would change that mechanism but until they do gemstore items are about the only way to solve the problem.