sks stock spring

[Ruger007]

I am taking apart my Chinese sks stock to possibly refinish it, I took of the recoil pad and found a large hole through the center of the but stock with a large spring inside. What is this spring used for? It has a hard rubber/plastic pad.

 

[Speckfire]

SKS recoil pad? I'm assuming its a sportster version of some sort. The spring there is used to push on the cleaning kit cartridge inserted there through the original butt plate that had a trap door access.

Here is a cutaway pic

 

[Ruger007]

That is probably what it is for. Just it has a plastic pad on it.
The gun just says 'made in China', 'SKS 7.62X39' no markings anywhere else on the gun. I got it about 7 years ago.