In military weapons training (and I'd even bet law enforcement), there is a well known expression: "Lock and load." Meaning, place and lock a magazine of rounds in the firearm, then load a round into the chamber. (U.S.M.C. Ooh-Raah!)
Unfortunately, there are some judges who either don't have personal knowledge of the issues they rule upon, or are judicial activists.
I don't know if one could call that "shakey ground" when it is common knowledge within all branches of the military. More like a crap shoot of getting an arbitrary, and erroneous decision.
It is also unfortunate that most attorney's don't know, or just wont raise the arguments they should be for their clients. Another excellent reason to learn the applicable laws, so as to properly instruct your mouthpiece (the attorney) or litigate the issue yourself.
If it were I and faced with the issue, I'd be doing a Request for Judicial Notice of this phrase and get it on record as a matter of common knowledge of military (and highly possible law enforcement) fact.
A chambered round is factually what loaded firearm means.