24" - 18" = 6" .... 6" x 25fps/inch = 150fps.

This is a TREMENDOUS, HUGE difference. An 18" barreled NE is an abortion from the ballistic perspective alone. I won't do the math, but that 500 or 577 or whatever didn't have the umph to push that bullet far into the head of any elephant.

Penetration potential is a simple mathematical proposition. You need a combination of energy, derived from velocity, and bullet weight for frontal area, or SD. Most combinations that work and are shootable are known. Bullets shape may have some influence, material, etc, but moving downward out of the box for velocity is a recipe for failure. As an example, the preformance of a 500gr Woodleigh solid at 2050fps does not compare to the performance at 2145fps. You would hardly believe that the same bullet out of the same rifle produced such different results. On the other hand, too much velocity should be traded for more bullet diameter and weight, imo.

Few of the big bore NE rounds, in real actual rifles with typical and proper length barrels - 24" - 28", produce velocity much beyond what is needed to do the job.

And there is the beauty of it. Rather than produce velocity which leads to more penetration than required, they push larger and heavier bullets for the same or similar recoil. The better to stop an elephant.

2300fps is the factory nominal velocity of the 416 Rigby and the 500/416, and the velocity at which your 500/416 will be regulated. So 2703ft/lbs of energy or so is what you will have to work with.

Big bore definition (John Taylor's) = 450+. Large medium bore = 416. Medium bore = 375 - 318wr.

If you are comparing the 500/416 or 416 Rigby to the 375H&H, then it is a different ball game.

As I mentioned earlier, I chose bigger and smaller than the 416 because I suspected that more was needed or less and the 375 is legal if nessecary because of ammo or rifle issues with the big bore. I am happy with my selections, they have worked well for me and I feel no need to change things, which is actually pretty remarkable.

My comment regarding the 416 being neither fish nor fowl was not meant to be a slight, just to point out that its strength lies in verstility, and not in specialty. It is heavy for an all rounder and light for elephants. The same could be said of the 375, but it is lighter for the smaller stuff (good) and even lighter when considered for elephants (bad) or buff.

In the end, it is your choice and your rifle. I am merely trying to point out that what the rifle will be called on to do, and do most often, is a critical consideration.

I will repeat though that not every bad situation provides even the opoortunity for a successful brain shot and no ones' shooting improves with a pissed off elephant busting through the bush and bearing down from seven or eight yards. Those who merely chant, "... if you hit them in the brain it isn't an issue..." need a does of reality.

JPK