A 155 mm compound gun barrel with full-length integral mid-wall cooling channels was manufactured and connected to a purpose built heat exchanger. Laboratory testing of this system was carried out using electrical heating jackets applied to the outer surface of the barrel and an internal electrical chamber heater to heat the barrel as uniformly as possible along its length. A series of tests were then carried out consisting of first heating the barrel to a uniform temperature of approximately 80°C followed by switching on the heat exchanger and monitoring the rate at which the barrel cooled. The purpose of these tests was to determine the optimum cooling characteristics of the system by studying the effect of different coolant flow rates combined with one or both radiators functioning and also the effect of using different cooling fluid solutions. Having derived the optimum flow rate and coolant solution combination a further cooling test was carried out with the heat exchanger configured to these optimum values and with the barrel heaters operating at maximum capacity. Finally a natural cooling test was undertaken where the barrel was uniformly heated to 160°C, the heating jackets removed and the barrel left to cool overnight. The results from these tests prove that natural cooling is dramatically slower than forced mid-wall cooling.