Check out this video by ESEA which compares the first bullet inaccuracy between CSGO weapons and CS 1.6 weapons.

0:15 Testing method
0:50 CS: GO M4A4 vs CS 1.6 M4A1
3:00 CS: GO AK-47 vs CS 1.6 AK-47
4:10 CS: GO Deagle vs CS 1.6 Deagle
5:30 Final results