I picked up a really clean no4 mk1 . This gun has a 4 digit serial number with "K" at the beginning . It also has 1944 on the but socket next to the serial number. The serial numbers on the receiver, bolt , magazine and forgrip all match. The only other marking is "UK" at the front of the receiver. The other thing is the bolt handle is hollow like a number 5. Just wondered what you guys can tell about this gun.