There's a few blacksmiths you can rely on to make arrow heads as exact as possible to surviving artefacts. Hector is one of them. In some periods, barelled shafts were used, so the socket will reflect that. Lloyd is correct, in saying the shaft comes flush with the OD of the socket. I use a pencil to guage the depth of the socket, then mark the shaft to that depth. A small pipe cutter from a hadware shop is useful for cutting the shoulder on the shaft. don't cut too deep as that will be where the shaft breaks.