Well, a couple of web pages I came across stated that the SKS was derived from the AVS. Just out of curiosity, any differences between the SKS and the PTRS other than calibre?The SKS was developed from the PTRS-41 anti tank gun design.
I can tell you from experience that the SKS is a fairly close copy of the PTRS41. I have a PTRS in the safe and taking it apart you wouldn't know the difference in parts except for the size. I've seen and fired and AVS 36 but it was long ago and I didn't get to take it apart. The only thing I remember that was common to the SKS is the tipping bolt.
here are a couple pics of the PTRS, one of it apart to show internals and the other sitting next to an RPD for size comparison. The RPD is a bit longer than the SKS....