On primative taming this is a lot harder but can be done! Use the ark calculator and add 10% the amount of boulders needed. Don't fire when he's throwing rocks as it won't register and don't space out your shots it's not needed! Use stone pillars to trap it and if it's a high level get someone to replace the pillars as you're fighting. Two catipults are preferred.
For some reason, after the latest update, X-rock elementals (haven't checked other variants) are no longer tameable. Whenever you knock them out, they don't eat and don't have a taming bar. Forcetame also doesn't affect them, so I believe it's a glitch