Bullets are a few thousandths of an inch bigger than the barrel so they will seal against it.
But the bigger issue is that by their very nature, entry wounds only can give a general indication of the size of the bullet. Bullet fragments are a far better indication.
This whole thing stinks. The liability tail for any local government agency who was anywhere near this debacle is going to be stunning. People on the government side must be frantic in their attempts to contain it.
Every level of gummint, local, state, etc. coast to coast is broke. One reason this is being dragged out is they can’t afford to pay. Notice the lottery winners in Illinois are being stiffed?