In this paper, outage performance of full duplex physical layer network coding systems under residual self-interference over Nakagami-m fading channels is investigated. Physical layer network coding technique and amplify-and-forward method with variable-gain relaying are used at the relay node of the proposed system. End-to-end signal-to-interference-plus-noise-ratio is derived for the equal power transmission at the source and relay nodes. The outage probability expression is obtained in a single-integral form by using cumulative distribution function approach. The analytical results are verified by Monte-Carlo simulations.