There’s a specific reason the actors aren’t supposed to check the gun. They cannot do anything that might fuck with a prop and fucking kill someone. They are to only use the weapon they’ve been given as instructed. It’s the job of the master armorer to ensure that all weapons, prop or otherwise, are properly handled.
This is protocol so it’s clear who’s at fault when an incident like this happens because they can just trace chain of custody. If Baldwin had checked the gun or handled it in any way other than instructed, he would be liable.