Even with black powder, too much, a barrel obstruction of not fully seating the ball could lead to tragic failure. The new higher pressure black substitutes and now smokeless powder model muzzleloaders have merely increased the likelihood that somebody will screw up. I myself have been distracted while talking to a person at a competition and accidentally dumped a second charge down the barrel. Forunately at competitons charges are usually so low that a double charge isn't dangerous. Sure I caught it, when I seated the ball.
The danger of some conicals is that if the gun is carried muzzle down, the bullet could slip forward (Happened with civil war minnie balls in muskets also) Then it is a barrel obstruction. As I said when I intitially posted a reference to thhat incident, it is scary when newbies read about posters saying they use exceptional charges of subs powder sticks and bullets. The newbies' gun could have been made in Pakistan for all we know. Or maybe a Spanish gun with a design defect or manufacturing defect. A well known Muzzleloader writer was boasting about his 3,000 ft velocities and how round ball shooters were inhumane to game. While he was actually pushing in-lines for a manufacturer, some folks are reading magnum loads are necessary and are unintentionally overloading or mis-loading their guns.