If the Duskblade Sect already knew about the mana oil, and they could make it, then there was no reason to hide it from Amie. The final changes that he had made were something that any mage could do, if they knew how, so it probably wasn't even unique to him.
Just not widely publicized, so that others didn't copy the technique and start to compete with the ones who had figured out the trick.
Dominic took out the oil he had used for the last one, and filled the tubes for the oil bath enchantment of the rifles. Normally, he did one at a time, but there was really no reason that he couldn't heat and dunk all ten, as long as he was charging the mana in the oil beforehand.
It was a simple process, made for human smiths with no affinity for magic. Nearly impossible for him to mess up.
Amie stared at him as he worked, heating the rifles so the mana core stuck to them, and then dunking them for their magical upgrade.
