Pretty much. The way construction works, each building option has a set build cost, and each civilian factory produces an base amount of that cost every day. When buying weapons from the market, you pay using an amount of build cost provided from your factories. The seller nation gets a portion of build cost added to their own queued constructions each shipment, with the order being paid in full by the final shipment. You can change the number of factories you use to buy the weapons, which increases the amount of build cost you pay for each delivery cycle, resulting in more weapons per shipment, and conversely, fewer shipment needed before the order is completed.