Here is an interesting post from a guy by the handle of Muledeer over at the 24 hour Campfire forums. Many who visit that site will know him and his level of experience and expertise when it comes to hunting and shooting. It's a comparison of the 308 and the 300 win mag.


Was just down at the first annual Charlie Sisk Rifle Shoot in Texas, and was in charge of an experiment comparing the .308 Win. to the .300 Win. Magnum at 400 yards. Charlie provided two rifles identical in every way--Model 70 action, barrel, McMillan stock, scope (a 4-12x Kahles)--except chambering. One was a .308 and the other a .300. Ammo was Hornady factory with 165 Interlocks.
The experiment was simple: I zeroed each rifle 2" high at 100 yards, then shot them at 400 measured yards to how much each bullet was affected by drop, wind, etc. The wind was gusting up to 15 mph and I did not attempt to compensate at 400 yards, firing a 3-shot group with each rifle over a forend rest (not a full benchrest setup with rear bag) simulating field conditions. I called one shot in each group out about 2", otherwise all looked good.
We could not tell which shots had been called out. Groups were almost identical at 8-9 inches, strung mostly horizontally due to the wind. The .308's bullets dropped about 7" more, and drifted maybe 2 more inches in the wind. But every shot from both rifles would have landed in the lung area of a big mule deer at 400 yards, if the shooter had held the correct amount high--no matter which rifle was fired.
The entire group from both rifles measured a little over one foot, with most in under 8" inches. In fact, if we hadn't known which rifle fired which bullet, it looked very much like one group.
Admittedly, "tuned" handloads, a better rest, and a very calm day would have resulted in smaller groups. But smaller groups would have resulted in even less difference in trajectory from the highest and lowest shots. Which group came from which rifle would have been more obvious--but any of the shots would still have killed a mule deer with the same hold.

I'll just make one more note. I have used various .30 caliber cartridges over the years, from the .30-30 and .300 Savage up to the .300 RUM. In general even the .308 and certainly the .30-06 have done fine on big game out to 450 yards, which is as far as I have personally ever shot at anything larger than a coyote.
There may be some advantage in the bigger .30's in penetration with heavier bullets. But every animal I've ever shot with cartridges such as the .308 or .30-06 has gotten a hole right through all the vital parts. The bullet was either found under the hide on the far side, or went all the way through. On the longer shots with these "smaller" cartridges the bullet has always been a 165 or 180. Since all the animals were hit right, none went over 30-40 yards after the hit. Some went straight down.
Therefore, it has been hard for me to grasp how using a .300 magnum on the same shots would have resulted in deader animals.
Not that I am giving up my .300 magnums. I own three at the moment, an H&H, Winchester and WSM--and I plan to hunt elk in Colorado this fall with a .300 Weatherby, a cartridge I already have some acquaintance with.
I just fail to see the vast gap in performance that some claim between the "ordinary" .30's and the the bigger ones. In reality it appears to be a "cline," a graded shift rather than a firm division in performance. But then again I quit believing in foot-pounds as a real indicator of "killing power" many years ago, after having shot quite a few animals and mostly discovering that if their pumphouse got punctured, it didn't matter much whether the puncturing was done with a .270 or a .338.
I also quit believing that we somehow "need" a minimum of 200 grains of bullet to kill anything bigger than a caribou. This is because too many animals died from the correct application of lighter bullets. The big factors appeared to be correct bullet placement and penetration, not exactly how much the bullet weighed, or its diameter, or exactly what percentage of weight it retained.
But, as always, that's just one person's opinion around the Campfire