Not really. How live ammo ended up on set should in no way affect his culpability (unless maybe it ended up on set with the purposeful design of causing a firearm accident, but even then I’m not sure…). The only thing it might be useful for is attacking the credibility of whatever government witness had anything to do with the… mis-filing. Whether this by itself is enough to constitute a Brady violation is beyond me. IAAL, but IANACLLTPLINM (I am not a criminal lawyer licensed to practice law in New Mexico).
Although I was just in Las Cruces a couple nights ago…
That said, I wouldn’t be holding my breath for a dismissal on this alone.