I'm having trouble doing this. I was able to enchant one peice of gear to a 25% reduction in spell casting, but the next enchant is less. Using a Grand Gem on dragon scale gear. Hopefully I am just doing someting wrong, but this sounded too good to last.

It's very much possible. Perhaps the grand gem had a lesser soul in it?

That's good news Fleapants, I'll get some new gems and make sure there are grand souls in there! Thanks

What flepants said. Make sure it says grand soul gem ( grand) as opposed to something like grand soul gem (lesser)