There should be a function that allows you to look down the weapon at an angle without using the attached optics for use in close quarters.
For Example:

Riflemen with a 4x32 on their M16A4 are at a disadvantage when breaching buildings. Looking down the weapon at an angle wouldn't be too far from realism as that is whats taught at the School of Infantry in the Marine Corps.

It could be implemented with a toggle or hold down bind.