This was my very fisrt gun ever. I would like to know what series it is and when it was made. The numbering is wierd to me, unlike most other military guns. The reciever has a serial and that is the only time this number appers. On the underside there is a 27 and 73. Most other parts have either one of those numbers or both. The rear sight has three completely different numbers that dont correspond to anything else. Is that the way japanese guns are? Thanks for any help.