I have heard of this happening and have experienced it.
The first year or two of producton used a firing pin spring until some Russian bean counter decided that by using hard primers they could do without it.
I wish there was a titanium firing pin with a spring, but there isn't as far as I know.
Also, check out
www.simonov.net
There should be more on this there.
In any event the advice to always keep it pointed downrange goes double for the SKS.