All the SKS's have milled receivers ... The Russian 1950's sks are much nicer firearm then the later models . Around 1956 57 Russian stopped manufacturing but it seems they were providing parts for the Chinese SKS .
I have 2 Russian and a early Chinese and it has Russian parts that are factory serial numbered .
I also have a 100 dollar Yugo shooter and its a great beater gun , too bad the days of cheap military guns have gone away .