Given the question, the answer seems to be a simple one - the more efficient cartridge is more fficient.If a person was to take two cartridges that have the same case capacity, but one is considered more efficient than the other. What are the pro's of the more efficient case?
So many variables to go along with “cartridge efficiency” from primer used to powder, barrel length, just the tightness of the barrel bore, throw in a little neck tension can even change things up.There is no such thing as cartridge "efficiency" as Handloader proved several years ago with their 300 WSM vs 300 H&H test.
Roy tried to peddle this BS in the 1950s and people fell for it. They still do.
The closest thang I can figure out what your talking about would be something like this. Let’s compare a 7 Rem Mag and a 7WSM. The 7 RM holds 83.2 H2O and the 7 WSM hold 83 H2O. So if Winchester’s claims are correct and they can get the same FPS out of the WSM as the 7 RM with grain per grain bullet weight that would be 1% more efficient. You get the advantage of a shorter rifle. The 7 Mag would need a 26” barrel to achieve the same ballistics as the 7WSM with a 24” barrel. I thank that’s what your talking about. Hope this helps.If a person was to take two cartridges that have the same case capacity, but one is considered more efficient than the other. What are the pro's of the more efficient case?
Just to add more confusion ask yourself which cartridge is easier for you to shoot accurately. (How hard does it kick)Long winded, and forgive me if you already know this.
As a reloader, cartridge efficacy is what gives me the best brass life, minimal maintenance, and outstanding performance. Some of the things that enable that are 35° or 40° shoulders, long enough necks for good bullet seating and minimal runout, slight taper for easier extraction without increasing rearward force on the bolt face, excellent magazine fit and feed capability, etc. These are many of the things that P.O. Ackley did in his case modification experiments.
An internal ballistician can tell you about efficiency. Borrowing a page from the Manhattan Project, if you really wanted to maximize the efficiency of your cartridge, you would "shape" the powder charge and load the cartridge with layers of powders of different burn rates and charge densities, focusing the shock wave. Problem is, you'd probably pulverize the bullet before it even left the chamber. Bullets are cheap. Quantity thereof and the quality of their use tends to win.
Seems to me, in your thirst for efficiency knowledge, you are asking about same powder charge, same bullet, different velocities. You may well know, the only way to test this would be same barrel/powder/bullet etc. I read posts here and on other forums where people are loading cartridges like 338 LM with the same powder, charge, bullet weight, primer and brass that I use, in a barrel 2" longer, and they're getting 200 FPS more muzzle velocity than I do. I scratch my head and wonder, WTH am I doing wrong? Mind you, their rig might be a Defiance action with Krieger or Shilen barrel, same twist and mine is a Savage 110BA. So, no matter what the cartridge might be capable of, YMMV.
All that said, I offer this comparison of 7mm Cartridges, the first two with similar case capacities, for your review:
View attachment 196530
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