A surgical instrument for laparoscopic and endoscopic clinical procedures simultaneously severs and staples tissue clamped in an end effector comprising an elongate channel, which holds a staple cartridge, and a pivotally attached anvil. An E-beam firing bar engages the channel and selectively engages the anvil during distal firing movements, wherein the tissue is severed and stapled driven upward from the staple cartridge to form against the anvil. In particular an upper pin of the firing bar is disengaged from the anvil before firing. A ramped transition from an anvil to an anvil slot avoids misfiring when the end effector has clamped too much tissue, yet assists in successfully clamping a slightly excess amount of tissue.