Nonlinearities in a structural system make the use of model updating methods developed for linear systems difficult to apply nonlinear systems. If the FRFs of the underlying linear systems in a nonlinear system could be experimentally extracted, then the linear model updating methods could easily be applied to nonlinear systems as well. When there are complex nonlinearities in a structure together with frictional type of nonlinearity, linear FRFs cannot be accurately obtained by using low level forcing. In this present work, the model updating method-Pseudo Receptance Difference (PRD) method-recently developed by the authors for nonlinear systems, is applied to the gun barrel of a battle tank. The linear FRFs of the nonlinear gun barrel of the battle tank are obtained from measured nonlinear FRFs, and simultaneously the nonlinearities in the system are identified. Then the inverse eigensensitivity method is employed to update the linear finite element (FE) model of the gun barrel. Finally, in order to demonstrate the accuracy of the updated nonlinear model, the calculated and measured FRFs of the gun barrel at several different forcing levels are compared.