The actor wasn't named by SAG specifically, but he was most certainly alluded to in this new statement they put out slamming the decision to prosecute him twice in this case. The union made clear ... knowing how to handle firearms is NOT an actor's job, from their POV.

They write, "To the extent that the charges filed on January 19 are based on an accusation of negligent use of a firearm predicated on this or any actor having a duty to inspect a firearm as part of its use, that is an incorrect assessment of the actual duties of an actor on set."

Then comes a haymaker, with SAG adding ... "An actor’s job is not to be a firearms or weapons expert. Firearms are provided for use on set under the guidance of multiple expert professionals directly responsible for the safe and accurate operation of that firearm."

SAG goes on to say that the procedure for safe use of firearms on set is clearly laid out in their rules and guidelines ... but they explicitly point out that a performer is not and should not be tasked with making sure the weapons used are dangerous or live.

Basically, there are experts for that type of thing on set ... and SAG is making that clear in no uncertain terms. It's a huge win for Alec as far as optics are concerned -- he's been making this point all along, and now ... SAG-AFTRA is confirming he is, indeed, correct.

You'll recall ... Alec was hit with a new involuntary manslaughter charge in the 'Rust' case -- and he's supposed to answer for it in court on Feb. 1 during an arraignment. Alec and his attorneys already responded to that, noting he has a right to speedy trial ... and wants to exercise that in this case, not wanting to drag it out further.

Meanwhile, the armorer from that movie -- Hannah Gutierrez-Reed -- is facing her own criminal charges in the matter ... although she too has pleaded innocence/ignorance over what led to Halyna Hutchins' death.