Heavy sledgehammer for grip

We’ve been using heavy sledges for grip work at our gym since I got some in the summer. Here’s one of DeFranco’s athletes training with them, definitely suggest it for strongman training.
DeFrancosGym.com: BIG Jeff Wills performs BIG BOY Sledgehammer swings! - YouTube!

Would associate that more with conditioning,if I were to make grip stronger I would lube up a kb and bang out some heavy swings;you would see a much greater increase of grip strength from that.