I agree with James B. On paper they make look fairly identical but with on game performance the 6mm wins hands down. That little edge it does have seems to make a world of difference to me. Once i shot the 6mm i sold my 243 and haven't looked back since . I just wish everyone knew how capeable the 6mm is. The selection in guns and ammo for this caliber is very poor, but one thing is for sure performance isn't poor to say the least.