Richard Harland , professional Elephant culler did an article about the .505 Gibbs Magnum rifle which he was using. Richard is a person who has used both the .458 Winchester Magnum ( a Department issued Mannlicher Shoenauer made anytime from 1958-60 ) and a .505 Gibbs Magnum ( an Original 1927 era George Gibbs Rifle and his personally purchased weapon ) . Having shot Elephants with BOTH calibers , he mentions in an article that he can definitely tell a difference between the stopping power of a .458 Winchester Magnum and a .505 Gibbs. He recommends the .505 Gibbs Magnum . Clearly , he has his reasons.
For the .458 Winchester Magnum , he would use handloads : 450 grain Monometal bullets ( Since 500 grain Monometal bullets would jeopardize case capacity to dangerous levels )
For his .505 Gibbs Magnum , he would use 3 loads : He started with vintage 525 grain Kynoch full metal jacket round nose solids . Then he went on to use 600 grain Barnes full metal jacket round nosed solids. I was told by a fellow member on these forums today who personally knows Richard , that Richard's final choice for his .505 Gibbs Magnum became Solid Brass 600 grain Meplat bullets which he himself would cut from Brass Bar stock .
Regarding the 400 class calibers , they are generally very good for the Job . But there are times ( albeit rare ) when the stopping power of a .500 Is Beneficial over the .400 class . They are documented examples of a .416 Rigby failing to kill an elephant even with 2 VERY WELL PLaCED solids ( one through the ear hole and one frontal brain shot ). A Book called " White Hunters " which l possess , does an excellent job in showing how many times a .470 Nitro Express failed to stop an elephant , hippo or lion or cape buffalo. And let's not even begin to talk about the .458 Winchester Magnum

Tony Sanchez Arino owns both a .416 Rigby and a .500 Jeffery made for him by Harald Wolf . He can clearly tell the difference in penetration and stopping power between the two cartridges .For Elephant , he prefers the .500 Jeffery loaded with 535 grain Kynoch full metal jacket round nose solids.
Me myself ? I use a .375 HH Magnum ( I own two : A Winchester Model 70 and a BRNO ZKK - 602 ) , but largely because l haven't learnt to handload yet and .375 HH Magnum ammunition is widely available. Someday, I will get a .500 Jeffery Hambrusch Bolt action Mega Magnum rifle with a DETACHABLE MAGAZINE or a .505 Gibbs Magnum built on a BRNO ZKK - 602 action for me , depending on my mood.
Now , l will relate a personal observation , made by myself on stopping power . I have hunted 4 Australian Water Buffalo till now and have seen MANY hunted over the years . Let me use my 2013 experience as an example. Rifle used : Winchester Model 70 in .375 HH Magnum. Ammunition : Kynoch Round nosed full metal jacket 300 grain solids . I shot the Buffalo In the shoulder aiming for a heart shot . The 300 grain round nosed full metal jacket bullet broke the Animal's foreleg , but distorted / deformed before it could reach the heart. Up until then , l had always read books about how Bufaloes couldn't run with a broken leg. Boy , was l wrong . It got up . I quickly took a Double lung shot at it , since the double lung shot is the widest target. The Animal went 80 ( ish ) yards , blowing blood through it's mouth and nose before collapsing .
Now , it so happens that l also saw a .470 Nitro Express Double Rifle loaded with 500 grain Kynoch Round nosed full metal jacket solids being used on heart shots and lung shots for Australian water buffalo , as well. The shooter once aimed at the Buffalo behind the shoulder and fired. In One shot , the 500 grain solid reached the Animal's heart .
On another occasion , he fired at the Animal from a broadside position using a double lung shot . The animal this time started staggering and blowing blood as if it's mouth was a fountain . In 35 (ish ) yards , it completely dropped , raised it's head a little and then just gave out. Butchering the animal showed that the damage to the lungs was substantial.
Now , let us compare this with my .375 HH Magnum's effect in the 2013 buffalo .
The animals shot were of roughly the same size. All three were Bulls shot at 40 yards. All three were shot using Kynoch Round nosed full metal jacket solids. So why did my heart shot fail and result in a distorted 300 grain full metal jacket bullet , while Evan ( my friend ) managed to reach the heart ?
Why did my lung shot allow the animal ( already wounded with a broken fore leg ) to go roughly 80 yards , while Evan's lung shot caused it to drop in less than 40 ?
Aside from the weight and caliber of the bullets , l cannot think of any other alternative explanation.
Of course , in practicality , l don't consider the Buffalo dropping dead at 80 yards to reflect poorly upon the .375 HH Magnum. No. I was very happy with the performance ( on the lung shot at least ). But in my non scientist , layman's views , there IS a difference.
Of course , shot placement is more important than caliber. I would rather use a .416 Rigby which l can accurately use than a .505 Gibbs Magnum which l miss with.
To conclude , as a client hunter , a .375 HH Magnum is probably all l will ever need as l have a PH with heavier artillery backing me up. But if l was ever hunting Elephant or buffalo alone , l would hands down find a .505 Gibbs or a .500 Jeffery Instrumental.
Hoss Delgado