I pretty much agree with everything here except changing the ejected casing on the ammo UI to a full bullet. I side with Harvest - most people I know would expect just the empty casing and not the bullet as well.
That being said, perhaps some additional effects such as a short-lived glow for non-penetration bullet/energy projectile impacts on metal would be cool in addition to being able to vary bullet hole size.
@Panda3d this suggestion pertains to the currently implemented bullet holes, as opposed to full obstacle destruction that you see in games like R6S. Personally I find R6S to be way over the top in this regard, and would much rather have only very weak surfaces like glass and plywood be broken like that, unless explosives, anti-materiel weapons, or heavy melee weapons are involved.