NGPC regs only state a minimum ft/lb for legal weapons for rifles.....
"rifles that deliver at least 900 ft. lbs of energy at 100 yards;
handguns that deliver at least 400 ft. lbs of energy at 50 yards;
muzzleloading rifles .44 cal. or larger;
muzzleloadering muskets .62 caliber or larger, firing a single slug;
shotguns of 20 gauge or larger that fire a single slug;
crossbows that have a draw weight of 125 pounds or more.
Semi-automatic firearms capable or holding more than six cartridges are NOT allowed."
I am pretty sure .223 WIN will do that...... lemmee see 3,000 x 3,000 x 55 = (9,000,000 x 55) = 495,000,000 / 450436 = 1,098.9followedbyabunchainsignifigantdigits ft/lbs. So a 55grain bullet pushed to 3,000 f/sec is LEGAL. Ethical? Not in my book, unless it is designed to hold together so it will penetrate.
As I have said elsewhere, "Deer are not armored vehichles. Poke them in both lungs and they will invariably die in short order."
Do I think .223 for deer is a good idea? (dons flame suit) No. Not a lot of margin for error there. Do I think it should be illegal? NO. No law will make a determined man not do dumb stuff. That and there are too many laws already.