Hi Guys I was thinking of getting myself a 500/416 double barrel rifle for the big 5. Question. Which one load only should I use ( the 410 gr or the 450 gr from Norma or other ). I like to get one load and sight it in for the life of the rifle. Also, why was the 500/416 ever invented. What's the advantage of this load compared to the 416 Rigby or the others.