When comparing the type hei rifle in the tech tree and the type hei auto rifle (in this example I use the lmg variant) the slide on the standard rifle moves a little slower making target acquisition harder, see if you can notice:
This is probably because of the higher rate of fire of the auto variant, meaning in full auto the slide wouldnt match the speed of the gun firing.
But in game it just makes the type hei (not full auto variant) more annoying to play,(a simmilar case can be seen with the type ko rifle).