If it's anything like the one on jb_sand maybe don't move inside it until you launch as it kills if you do. I managed to launch out of it the other day, fun game is to try get Ts to either land on a ladder or you can surf down the windshields of the cars in the parking lot.
For my case in New_summer, i was jumping inside of the mancannon praying i wouldn't die and it launched me so no clue.
Could be something to do with your position in there when it launches, maybe stand away from the button or close to the side it opens up at.
Or maybe in the middle?. Why do i feel you gotta be on the T side so the Mancannon can work but am not really sure i need to keep trying while am on ct.
The cannon on new summer, I’ve seen it work like twice in all my time playing. Every other time it just kills the player the one on sand is consistent in working
Not to bring up other servers but on the other jb server (not hell) the canon works on new summer every time, so maybe it's to do with the servers settings or map version