The Charged Void metal Cap is a wand cap component added by Thaumcraft 4. Any wand created with these caps will incur 80% of all vis costs instead.
Crafting wand caps from Void metal seems counterintuitive since it seems to be highly resistant to magic, but counterintuitive is where you live now.
Your gamble paid off. The metal itself may be resistant to magic, but it channels with surprising ease. The magic does seem strange somehow, but it is probably just your imagination.