What "bump" are we talking about. Primary extraction is at the rear of the bolt. It is an interaction between the ramps on the bolt handle and the rear baffle. there is a normal gap between the rear baffle and the action. If it is too short you cant open the bolt easily due to the ramps engaging too early binding the bolt, where the lugs have not cleared the abutments before the ramp engages. Too long and there is no primary extraction due to the ramps not engaging soon enough or not at all.