I’ve killed a pile of deer and pigs with 223/5.56. I’ve killed them with everything from 55 Grain FMJs to 60 Grain Hornady soft points, to my favorite the 69 Grain Federal GMM. I’ve never lost a deer using a 223. I have lost pigs, but only because of poor shots and being unwilling to track them into thick cover at night. Sorry you lost your deer, but you didn’t lose him because of the cartridge choice.