In this paper we consider the design of unstable resonators for use on pulsed HF/DF chemical lasers. The limits on the resonator magnification, as set by mode-growth time requirements and parasitic oscillation, are evaluated and the predictions compared with experimental results obtained using a fast pumped transverse discharge HF laser. A detailed experimental study of the laser performance with a 2.2 magnification unstable resonator has been carried out for both HF and DF operation and optimum operating conditions for energy and peak power extraction defined. Time resolved studies of the multiline HF and DF laser emission spectra are reported. The system described should prove useful in experiments which require a high intensity focused beam.