Exactly.
What happened there is not a really textbook example of the fact that a blank still presents a potential danger even though it is a blank.
While I don't know for certain, I strongly suspect that hundreds of blank rounds were fired during the making of that film without a single one of them hurting anyone.
The sole reason that Lee was killed was that there happened to be something obstructing a gun barrel.
Once that was the case?
The blank round stopped being a blank round. It was a live round in two pieces that no one knew were both in play.