How do I tell if my rifle has matching serial numbers?

The K31's have serials numbers stamped on several of it's parts (See the complete list t the bottom). The most obvious of these parts is the receiver and the bolt (first ptc below), you can tell by looking whether or not the numbers match. These number are typically "stamped" into the metal although there are case where the bolt has been replaced and it's been "electopenciled" the match the serial number on the reciever. I can't show you a picture of an electropenciled bolt since none of my guns have them.

There are also serial numbers on the inside of the stock that can only be seen if you take the action/barrel out of the stock. This picture shows the serial number that is stamped inside the barrel channel of the stock.

BTW - The small stamping that you'll notice on the right shows the stock was made by SIG (Schweizerische Industriegesellschaft Neuhausen)

The underside of the upper handguard is also numbered.

The other parts that typically have serial numbers on them are:

Don't be alarmed if serial numbers don't appear on all these parts. Some could have been replaced due to wear on the original rifle or may not be visible due to wear.