If I were an ammunition manufacturer, and my ammunition is made-to-order, how would I calculate which customers get priority over others? Let's say there are 100 customers who make 100 orders of varying amounts. The first two orders are of 10,000 rounds each, the next ten orders are of 1,000 rounds each, and the rest of the orders are of 20 rounds each. In total, the two first customers ordered 20,000 rounds, the next ten customers ordered 10,000 rounds, and the last 88 customers ordered 1,760 rounds. The first twelve orders make up around 94% of all of the ammunition ordered, so 88 customers will have to wait for the first 12 people to have their orders completed. The problem arises when too many customers are unhappy with you because they're not getting their orders fulfilled. This, in turn, results in people being less interested in ordering from you and more likely to mention that you are a slow ammunition manufacturer, which will result in less sales, even from major buyers.

Which formulas would I use to determine the ideal order in which customers should have their orders fulfilled with regards to the ammounts customers ordered and the order in which all unfulfilled orders have been made? I don't think it would be fair to make it so that each order is completed in approximately the same time, either, and if a particular customer orders 1000 rounds first, and then orders another 20 rounds later, he should be treated as if he ordered 1020 rounds instead of one order of 1000 and then another order of 20.