SInce the change in character animations the character holds the weapons when prone way to up and close to its face.
This issue has been around for around half a year at this point .
the issue is mostly with the m16 and ak platform , both have the issue if you go prone that the holding position is way of the ground and makes the characters head go in to the gun,
this issue makes it unuseable for modders to add scopes as 90% of the time while prone the scopes end up in the characters head and it will bug it out.

the main issue here is that the mag is way to high of the ground and no person would actueel keep it up that high. on the m21 this issue is not there as the mag is way closer to the ground as the holding position is diffrent and is the only weapon without this massive issue.

i added the follow 3 pics for showcase
the m16 base game
the ak basegame with added scope . even mounted that much forward will still have the scope bugged out
the m21 to showcase that this is the only gun with the correct eye hight and this gun has 0 of the above issues
also added picture of the exp as that claimed ot have a fix for it or atleast would adress the issue

i really hope this can be fixt or changed as it would make our gameplay a lot better and actualy will help the modders and people to use and make more scopes without these issues