ObjectTemplate.SetTurnDev

MDT description

How much deviance to be added to a weapon due to turning:

x - maximum deviation possible
y - how much to add for each frame tilting up and down 
z - how much to add for each frame turning left and right 
w - how much to reduce per server-frame (30 fps)

All x-values (maximum deviation) of SetFireDev, SetMiscDev, SetSpeedDev, and SetTurnDev are added together.

Source and more details