300 Blackout hands down.. loaded with 110 gr Barnes black tips, 125 Gr SST's or BTIps are deadly on deer out to 200 yards... I have tracked a ton of deer shot with a 223 by kids (not expert shots.. these kids can shoot paper great but the adrenaline kicks in when the deer show up) I have taken a lot of kids hunting and will pick a 300 BKout loaded with the right bullet any day.. hell Im hunting wiht one this year.
