It's a 243 bullet for sureWas it actually a .243 bullet too? Or just an incorrect head stamp? Both rounds do use the same case after all.
Quite common......I've had on different round in federal ammo twice but worse yet I've had 338 federal ammo that wouldn't chamber.......I now pull my firing pun and cycle all ammo through my rifle at home and label the box accordingly........3 boxes of federal 210 NP, 338 Federal ammo and 4 rounds that wouldn't chamber......don't bother to call em as they'll send you a check for $2 or some such.