Thanks, everyone. The balls I have right now are .315. It seems odd to me as well that the mouth would be smaller than the inside dimension of the chamber but that was what I had found. The balls I have now do shear when I lever down, but then they flop in and out causing the gun to jam up.
I'll try a larger ball. Not sure how that would change anything but I'm game for it. I'm still thinking that camphering the mouth of each chamber so the mouth is slightly larger than the inside diameter is the solution. I'll let you all know what happens after I try a larger ball.
Thanks again. ~Craig