 The replacement was relatively easy, as the 105 mm is largely a rebarrelled version of the 84 mm and has a similar breech.Photographs of the prototype do show some change to the recoil cylinders between the two.A further design for the "Prodigal" requirement used a pair of the 120 mm recoilless rifles, as used for the WOMBAT, fitted with seven-round revolver autoloaders.