You can use tames instead of firearms to trigger the roar once they’re in shield mode. I recommend something that has a nice backing-up speed so you can bite without getting bitten.

Deinosuchus are what I prefer because they can’t be knocked back by an acro’s attacks or roar. They can be mounted again very quickly without requiring you to run far to the acro’s mouth. Only use the quick bite attack, not the giga bite (for fear of killing the acro). The damage should be dealt carefully, and you should be tracking the hits. Any other tame with these qualities will do well.

This can also be done quickly on a Pyromane, but be careful not to use the Pyro on the last round of dealing torpor. I’m not sure if the burn can mess up the taming effectiveness, but I didn’t want to find out. I use a firearm or pike to tigger the last roar in this case.

Good luck!! <3