Just read an interesting article on efficiency. Didn't catch the author. A little light reading at the magazine rack while waiting for a prescription to be filled. Seems the author had some free time and did the math for a whole bunch of cartridges at the 200 yard line. He calculated energy per grain of powder and Wooters L score per grain of powder. Didn't say if he made any attempt to equalize ballistic coefficient or not. I'm assuming that he was using factory ballistics charts of some sort.
The bottom line of his article was that the most efficient cartridge on both scales was the 35 Whelen. He also pointed out that the 358 Winchester, and the 350 Remington Mag were also in the top 5. And made the comment that the 35 Remington with spitzer bullets would also be in the same basic placement in terms of foot pounds of energy per grain of powder burned. I found it quite interesting that the top 5 was dominated by 35 caliber cartriidges. The only thing that bothered me was that when I did the math myself the 358 Winchester came in first and the 35 Whelen and 350 Remington Mag tied for second.
I've had a pet theory for a long time that there are some calibers have slight advantages over other similar calibers due to poorly understood effects of air turbulance during flight. Engineers and Scientiists are still working on getting mathematical fomulas for all of the interesting aspects of Fluid Dynamics. Air being the fluid in this case. These effects are why Wind Tunnel testing are still so critical to to aircraft design, race car design and bullet design. There are just some aspects of Fluid Dynamics that can't just be predicted by the currently available formulas. If these things were completely understood Wind Tunnel testing would not be needed as you could just plug all the known variables and predict the results. One caliber that seems to be more than would be expected is the 6.5mm (0.264 inch) bore diameter. I have always thought of the 0.375 bore was another of those that performs just a bit better than expected.
My recent experience with the 0.358 bore leads me to believe that it may even be more of a "magic" bore than the 0.264 and the 0.375. The BLR in 358 Win has been a really wonderful experience. The "felt" recoil is amazingly light. The only 35 caliber that I've heard recoil horror stories about is the 350 Rem. Mag. in the original Model 600 and the Model 660. My BLR with Nikon 1.5-6x42mm Monarch Gold scope weighs 7.8 pounds and the "felt" recoil is less than my Ruger #1 in 270 Win with a Lepould 2-7 Vari-X II that weighs 8.5 pounds. The muzzle blast is very mild, mostly due to a high expansion ratio. Max loads are burning between 48 and 50 grains for bullets in the 180 to 250 grain bullets using Accurate Arms 2520 powder. That charge wieght, of that powder, expanding into a 0.358 caliber bore and a 20 inch tube has fairly low exit pressure with almost complete combustion. The deep boom of the 358 Win is a lot more pleasant on the ears than the high pitched crack of the 270 Win. It should be noted that this Ruger #1 has the barrel shortened to 21 inches from the 26 inch tube it came with. While that makes for much a handier rifle the muzzle blast is awful. Even other shooters on the range ask what kind of a cannon is that?? And are usually quite surprised when I tell them it is a 270. Even though H380 is a relatively fast powder for a 270 it is quite the flame thrower compared to the 358 Win with an inch shorter tube. While I'm only using a couple more grains of powder in the 270 it just doesn't have the expansion room of the 358.
The most delightful aspect of the whole thing is the minor difference in trajectory. The 270 is usually thought of as a very flat shooter. A lot of people think the 358 Winchester is a short range proposition. But check out this comparison. This 270 is hampered a bit by the 21 inch tube. The Factory Ammo just barely breaks 3000 fps. With a 200 yard zero, this is 1.6 inches high at 100 and 7.4 inches low at 300. My best load out of the 358 is a 250 grain Nosler at 2400 fps. With a 200 yard zero, this is 2.9 inches high at 100, and 11.7 inches low at 300. SO THE DIFFERENCE IN DROP AT 300 YARDS IS ONLY 4.3 INCHES!!! I generally figure that in the field with a good field rest I can shoot about 3 MOA or 9 inch groups at 300 yards. So at 300 yards there is a 60% overlap in groups from the 270 and groups from the 358 Winchester!
At 300 yards I'm still getting 1,945 foot-pounds of energy with the 358 Win versus 1,480 foot-pounds of energy for the 270. So at 300 yards the 358 Win is delivering 31.4% more energy than the 270. At 300 yards the 270 has a momentum of 1.31 pound-seconds where the 358 Win has 2.08 pound-seconds. So the 358 Win is delivering 58.8% more momentum at 300 yards. Last but not least the initial frontal area of the the 0.358 caliber slug is 67.0% greater than the 270.
In summary using less powder, a shorter case, a shorter action, and a shorter barrel the 358 Winchester out to 300 yards has similar trajectory to the 270, more energy for increased expansion and ablity to destroy large bones, more momentum for increased knock down power amd penetration and more frontal area for increased wound channel diameter.