I built a TNT cannon with 80 focused charges. When firing at an angle of 45º i blasted off to approximately y=620, at which point my character acted like if it hit a solid ceiling, sliding sideways and falling. When i used half charge, i blasted off normally and hit a vector of y:1059,5.
Then i built a larger cannon with 160 charges, at which the full-blast cap was seemingly reduced to approximately y=310. Character instantly hits this height and slides parallel to the ground until coming to a halt and falling to the ground approximately 500m away from the cannon.
I attached a scheme of the observed trajectory. On multiplayer, all that happens is that after (latency) milliseconds the player is teleported back to the explosion origin with a speed of zero like if it never happened.