I believe it has been discussed many times on CGN forum but I've found these documents really useful, especially with the surge of SKS purchases and new SKS owners joining the gang there might be people asking what to do with their SKS carbines that shoot 10 feet high and 20 feet to the left (lol)
These are the official sight-in guidelines for Soviet and Yugoslavian armourers. Too bad I haven't been able to find the Chinese version but I'm pretty sure they are almost identical to each other.
Both guidelines require that you use the BATTLE SIGHT (III or 3), then shoot 4 rounds from a rested position at 100m, and aim at the CENTER of the BOTTOM EDGE of a black target.
The Soviet manual requires a black rectangular target (35cm x 25cm) attached to a white backboard (100cm x 50cm), while the Yugo instruction only requires a 25cm x 20cm black rectangular target attached to a white backboard of the same size.
After shooting 4 rounds, you gotta check your grouping. At least 3 rounds should fit within a 15cm circle. This makes sure your SKS has the Minute-of-Capitalist accuracy (5 MOA at 100m) to begin with.
Then, locate the center of your 4 hits by pairing 4 random bullet holes with 2 straight lines, connecting the 1/2 centres of the 2 lines with a 3rd straight line. The center point of the 3rd line is now the center of your hits.
Now, compare the centre of your actual hits to the theoretical point of impact, which should be exactly 25cm right above the point of aim. If the deviation of your actual impact vs the theoretical point of impact is less than 5cm, DO NOTHING. You're all set.
If the deviation is greater than 5cm, you will need to adjust your front sight post. Say if it shoots to the left, then you push the sight post to the LEFT. If it shoots high, you turn the sight post UPWARD.
For Russian and Chinese SKS:
Each full turn of the sight post changes the elevation by 16cm at 100m. Moving the sight post horizontally by 1mm changes the windage by 21cm at 100m.
For Yugoslavian M59/66:
The elevation adjustment ratio is 1 turn = 16.5cm at 100m, while windage is 1mm = 22cm at 100m.
Hope this helps, comrades.