i guess the .243 is illegal because you hunt in an area where only shotgun and pistol caliber rifles are allowed. Man that's crazy but something you have to deal with. If it were me, I would use the .44 over the .410. I have no experience with the .410 slug but I have shot a couple deer with a Marlin .44 mag rifle and also used 300 gr .44 bullets with sabots in my muzzleloader to take a few more. And that may be another option for you - a .45 or .50 cal muzzy which you can load down with 70 or 80 gr of powder giving you light recoil and sufficient energy to kill a whitetail.