Hi there,
Thank you for sharing the logic, that helps to understand what is causing the issue.
You’re almost there. I believe you’ve missed that “find look at rotation”:
If you’re changing the cannon’s pitch, this information should be feeding into the projectile calculation, however only the node “Suggest Projectile Velocity with Custom Arc” has such parameter exposed in Blueprint. Keep in mind that the cannon’s pitch of 0 - 90º equals to 1 - 0 in that node (“Arc Param”). So, you’ll need a “map range clamped” node.
In my timelapse video, I show how to use that node with a projectile launch at time 1:03
Hope that helps.