A decision was made to replace the six NR-23 guns in the nose with four AM-23 cannon with 225 rounds per gun that had a rate of fire 50% greater than that of the NR-23 and to totally revise the gun installation. The guns were moved to the very tip of the nose in a separate compartment made of heat-resistant steel and provided with a special blast deflector chamber to deflect the blast gasses away from the engine inlets. Two doors were provided at the bottom of the chamber to ventilate the chamber while firing. One problem occurred almost immediately during testing when the blast gases accumulated in the section where spent cartridges and links were saved and sometimes ignited. Occasionally this was strong enough to actually deform the chamber. The spent shell case section was thoroughly ventilated and muzzle brakes were introduced to successfully cure the problem.