In the event of a temporary shortage of a particular part, priority allocation of most parts is to complete rifles, then upper and lower halves, and then individual parts and pieces. We have carriers coming in almost daily, but MOST are going out in rifles and uppers. Some are still going out as parts, in date order from oldest to newest order.
Most upper halves (5.56) are shipping within 30-45 days. The more subs and upgrades you add, the more likely that something will be out of stock at any given time, which can add to the lead time.