I was visiting a local gun shop and noticed they had these Nice looking Zastava m70 rifles for sale they have been emailing me with falling prices since the panic wore off. But as I was looking I noticed a strange button on the rear of the reciever, that almost looked like a folding mechanism lock. It is the third nipple or looks like a rivet on the back of the reciever, and pushes left to right. You can see the top cover is notched where the button sits.
Forgive me if I am ignorant but of all the ak's I've seen including my Zastava PAP pistol, I have never seen this button and I am very curi