JDL here is one answer to yours question copied from one another forum:

"To explain let's back up to your average action like a Rem 700. With a round in the chamber and the bolt closed is the position we are concerned with. Like this the sear spring is pushiing up on the sear which is in contact with the angled surface of the cocking piece. This is forcing the back of the bolt up in the action. Can be as little as 0.001" or as much as 0.007" give or take a little. Reason is the Rem bolt is around 0.690" in diameter, while the raceway in the action is 0.705" roughly. This provides clearance for dirt, etc...
The Borden bumps are on the bolt behind the lugs and I think in front of the handle also. Using the same Rem #s for simplicity, they make the bolt 0.704" in diameter. That way in the locked up position, the sear/CP can't push the bolt out of square with the bore axis more than 0.0005" unlike the standard Remmy bolt being pushed out of square by several thousands. Clear as mud?"