please go back and read what you wrote?
You stated the mouth of chamber is smaller than the chamber dimensions farther in.
The balls work forward jamming the revolver.
If you were to champfer the opening (make bigger) would this not in turn exacerbate the problem? Yes it would.
Almost all BP revolvers are designed with an opening smaller than the rear of the chamber.
The smaller opening, causes the ball to be squeezed and compressed into the cylinder.
Causing a friction fit. Thus causing pressures to build up when firing to then expell the ball out at great force.
When seating the ball you should be shaving a nice ring of lead from all around the ball.
If not, then the ball is too small.
Are you sure you have a .31 and not a .36 (of any model)
Measure the opening of chamber. You want a ball anywhere from 2 to 6 thousandths larger in diameter.
But no, you do not want to champfer the opening with the condition you wrote about.
I have a .31 Colt Pocket pistol that I'm having issues with loading. The ball has a tendency to slip back out past the front of the cylinder causing the cylinder to jam. Near as I can tell from making a few measurements with calipers, the mouth of each chamber is .003 to .004 smaller than the inside diameter. I'm thinking chamfering the mouth would resolve the problem. I know there are tools for some various caliber cylinders but I'm not finding anything for any of the common BP pistols sizes let alone a .31. If anyone knows a source for such a tool or can suggest another method, I'd like to hear about it.