I have had problems shooting a less then full case of black in a .43 Spanish when I was a kid. It bulged the chamber enough that I had to drive the case out. But this was a Military rifle with a lighter barrel then what I use now. I rung a chamber with a .45-120 3-1/4" case full of compressed powder. I put the blame of a hang fire when that happen. I was at a muzzle loader match and a guy put a large walnut in his barrel when he shot a short seated ball. It can happen.
I breach seat my bullet past the lead in the throat but I do not use a wad in the case mouth. My load is compressed enough so the powder holds when I remove a .012" card that is flush with the case mouth that holds the powder when I'm on the road so it don't spill out. I have left that .012 card flush in the case mouth that would have about a 1/8" gap under the bullet base and sofar I have not had a problem doing this but I do carry a stick pin so I can remove that thin card.
In a straight wall case like the .45-70 and you put a heavy compression on the powder and the bullet breach seated ahead of the bullet by more then 1/8" I would think that heavy compressed powder is a solid mass like a wad. That might cause a problem when the air gets compressed between the hard powder and the bullet base. Cant say for sure that it could happen or not because I have never done it.
A short volume of compressed air between two solid objects will do a lot of damage.