Generally just go with what’s on the box. I can’t recall any stories from anyone about a NRP officer interrogating then about muzzle energy. That said, almost no .223 with less than a 20” barrel can make >1200ft-lbs.Ok so I looked it up. It must meet 1200ft lbs per MD law, some ammo BARELY meets that at 1293ft lbs. With out further research it wasnt stated what size barrel was used to achieve that. Also after watching ammo test I know it can vary easily by rounds in the same box. So yes .223 is legal but I wouldnt want to risk it if they really wanted to push it. I could understand using it for crop permit cause if the deer got away well its gone, but if trying to put food in the freezer id be using something with more put down power for sure.
It’s as much there to do things like catch poachers using 22lr as anything. Or something obviously not meeting the requirements like an M1 carbine (which is sad and silly because with soft points it works great on deer within 100yds.