Help with Mauser K98 Rifle

[sdmark777]

I have this Mauser K98 rifle. I don't know a lot about these rifles, so I hope someone here can explain this rifle to me. It is Chamber marked 243 and 1940 date. 243 code indicates manufacture at Mauser-Werke AG, Werk Borsigwalde, Berlin-Borsigwalde, Eichborndamm.

It has a plain non serial numbered and unmarked stock with no disc in the stock for bolt disassembly, instead a hole in the buttstock cap.

So, did this rifle originally have a stock with the disk and serial number?

Is this possibly an original later war military replacement stock or ?

A stock from somewhere else?

Thanks, Mark