Watching t'news this morning it seems like the weapon was an olde style revolver which would fit with the films era. That means it's likely to be a Colt Peacemaker, Colt Army, or something very similar from another manufacturer.
While manufacture of that type of pistol dragged on for many decades and they were later available in smaller calibers, that most likely means a .45 or 44-40 from the earlier years of production - a big, heavy round (they also used them in light rifles of the era) so no doubt it went through the poor camera woman, making a nasty mess as it went, over penetrated then went off on its merry way and hit the director.
I know Baldwin is only an actor, but gun safety should nevertheless apply to him - you're handing me a weapon, show me its clear/loaded with blanks before I lay a finger on it, exactly the same way any other conscientuous recipient of a firearm should.
Also the person handing the weapon to Baldwin should themselves have insisted that they be shown it is clear/safe/loaded with blanks nefore they themselves took possession of it. And so on. Lots of negligence at every stage, from the person who prepped the weapon, through everyone that then hamdled it, right through to Baldwin.
It also seems the armourer is very young, not that age is a problem per se, and this is one of her first jobs as a fully qualified armourer in charge. Seems she was also recently voicing her concerns that she was not ready/experienced enough for the role. Nevertheless, she signed on and took the coin, so I think I can see which way the blame will lie on this one, even though Balwdin by rights - though not by law - should have been himself insisting the weapon is shown to be safe before laying a finger upon it. These are lessons written in the blood of less cautious people, yet no one here seems to have paid any heed to them.
Even worse for her, it seems that there had already been 2 negligent discharges in previous days, and concerns about firearm safety were so great that some crew members had quit rather than risk being on set. Doesn't look good for her.