Squeezebore (which is when the barrel gradually crushes the bullet to a smaller diameter) 

has historically been applied on large scales,  such as a 30mm round crushed to 20mm.  Understandably it's reputation as a barrel burner might stem from this usage. 

I heard that some current rifle (I think the MR556) has a barrel which has an extremely subtle squeeze,  possible from 5. 7mm to 5. 5mm. 

I was thinking if you could maybe expand that slightly, such as reducing down to 5.2mm,  and benefiting from the improved ballistics.  

Obviously it would work better with custom designed 556 ammo. 

My Concern was accuracy,  because the newly crushed bullet surely won't retain its carefully crafted high BC shape?