To knock out, build a small stone cage. Place a foundation, a door and walls. Instead of using walls for the second, use door frames. Get in the cage, and shoot the Bronto from there. They can't damage stone, so no worries. When knocked out, I highly reccomend using Kibble. If you use berries, it takes ages. Don't use vegetables, they're better for making the kibble.
Brontos are a bullet sponging machine if found with correct base health and melee you will make raiding easier can get 150 Brontos to around 70k health and swiping it's tail can destroy x seeds hella quick