Why did't you do /disarm on him?
He could maybe have gotten the minigun from one of the mg DM areas

Even if he indeed got his Minigun from DM are, he still should be Permanently Banned for abusing the Minigun.

He is clan member, and Admin.

Admin should be trusted, know the rules, show a good example, and not abuse any thing.

If he is doing it, he isn't deserve to play. (Perm Ban)

Or at least demoted and kicked out from the clan.