A simple model of an axisymmetric tandem mirror without thermal barriers is employed to study the stability of ballooning modes which are confined to the central mirror cell. The central cell is treated as long‐thin with isotropic pressure, while the end plug is modeled by a line‐tying boundary condition. The scaling of &bgr;cwith the mirror ratioR*and the connection lengthLcis computed, and the sensitivity of these results to the magnetic field profile chosen is discussed.