Lynn, you brought up a good question. I didn’t respond because Greg has a better handle on the answer than I do. After all, I’m not an Engineering or machinist, just a knot-head hobbyist trying to figure this stuff out.
Thinking out loud about this radius, and I’m not trying to minimize it’s importance, but here’s my take on the operation of the breech block. On opening, the bb drops until it clears the front nose of this radius. At that point it can start tipping but really nothing forces it to tip until it hits the valley in the trigger guard. At that point it is force to tip. This being said, the link has a ledge that engages the bottom of the bb so it can’t try to straighten back up, it will also follow the bb as the lever is opened. See the disassembled picture, this picture shows the configuration of how it came apart. So on opening, this radius does very little, other than not letting the bb tip too far.
On closing, when the finger lever is moved to closing, the bb comes free from the trigger guard and raises until it contacts our radius which then forces it to start the closing operation. Looking at my drawing you will see the front nose of this radius is just below the bore centerline. So as the bb closes, and a shell is in the chamber, the bb will come up hard into this radius and cam a tight shell into the chamber. Once past the radius nose the bb can raise and close completely.
This may seem simple, and if I’m correct, also shows the importance of the radius is in the last stage of closing only and only a loose guide for the rest of the operation.
Please correct me if I’m off on these assumptions.
Bob