A surgical instrument includes a housing, a handle, an elongated shaft, an end effector assembly, a drive assembly, and an extension depending from the handle. The extension includes a proximal surface having a first proximal cam portion defining a first angle with respect to the longitudinal axis and a second proximal cam portion defining a second angle with respect to the longitudinal axis. Initial actuation of the handle from a non-actuated position causes the first proximal cam portion to contact the first portion of the drive assembly causing a first movement of the at least one jaw member, and a subsequent actuation of the handle causes the second proximal cam portion to contact the first portion of the drive assembly causing a second movement of the at least one jaw member.