It really depends on what the breakdown is and how many magazines he had and what the breakdownin ammo was. If everything was loaded ans laid out it could be done in a day that’s 10-12 hours, if you don’t care about keeping guns usable you could probably do it faster. It’s all about reload speed and managing heat, endurance would be a factor as well. You can pretty easily attain a 4-6 rounds per second with most guns, world record levels are more like 10 per secondwith a pistol. Bushmaster claims and effective 45 rounds per minute with their ar 15, which would be just under 10 hours.