Thought I would share a basic formula for calculating the difference in kinetic energy when you either increase calibre whilst keeping the case capacity the same( like necking up a case) or increase case capacity whilst keeping calibre the same( like comparing 30-06 to 300 win mag case sizes).
Its not perfect but makes a rough estimate and was handy back when you were trying to figure out what safe max loads would be for new wildcats.
basically as follows.
Increasing Calibre
1.The increase in kinetic energy when necking up to a new calibre is equal to half the increase in cross sectional area. So if say necking up( or comparing) a 378 weatherby to a 460 weatherby you take the .165 sq in of the 460( .458 cal and using area of a circle formula) divide it by the .110 sq in of the 378( 375 cal) which gives about a 50% increase or 1.5x as much. Therefore the theoretical maximum kinetic energy increase of a 460 over a 378 is half that, or about 25%. if you take max loads for a 378 wby which are about 6200ftlbs, you end up with 7800ftlbs for the 460.
Increasing Case Capacity
2. where increasing case capacity the % increase in kinetic energy will equal half the increase in max water case capacity. So comparing a 458 lott with its 108 grains to a 460 wby you have the 460 with about 40% increase in case capacity which should mean a 20% increase in KE. Running the figures on max 458 lott loads of about 6400ftlbs this gives about 7700ftlbs for the 460 which is about right.
Now again, its not perfect, the length of the bullet intruding on powder capacity, the fact when you neck up you may also increase case capacity and max load data running at different pressures will all have an effect. Also some of the special high energy powders that have come out will prevent a comparison to normal powders.
'But generally where all else is equal its works out and if you compare max energy loads of 308, 30-06, 300 win mag and 300 weatherby you will see that half increase jump as the powder capacity increases.
'And as you neck up say a 375 wby to 416 rem to 458 lott, to 470 capstick you will see the same half cross sectional area increase in energy along the way.
You can also do one calculation after the other to compare increasing both case capacity and calibre. Say comparing differences between a 338 win mag and some new 40 cal wildcat you are considering based on a 404 jeffery case or something.
I got shown this in the pre-quickload days by a weatherby collector Mike Mcguire from Sydney. He was incidentally one of the first fellas to import 460's back in the late 1960's( well before my time)/ Is it still useful, well not as it used to be. But it was handy back in the day when trying to predict what the max velocities might be for unknown wildcat developments. If you can estimate kinetic energy you can work backwards to get the velocity for given bullet weights. In the early days of the internet we were also using this to predict maximum loads and velocities with the old nitro express rounds on modern actions. For ecample running figures for the cavernous 505 gibbs on a Cz550 for the first time by comparing to known velocities with the smaller 500 A-square case.