Necked down ? The 308 Winchester and the 30-06 Springfield are both the same caliber, which is .308 caliber. The 308 Win. is almost a 1/2 inch (.479") shorter then the 30-06 Spr. The 308 Win. has a case length of 2.015 inches and the 30-06 Spr. has a case length of 2.494 inches. The 308 Win. and the 30-06 Spr. are completely different cartridges all together. The 270 Win. is necked down from a 30-06 Spr. The 280 Rem. is also necked down from a 30-06 Spr. but Remington moved the shoulder forward .051" of an inch so it couldn't be cambered in a 270 Win. The 35 Whelen is necked up from a 30-06 Spr.

The 308 Win. is inherently more accurite then the 30-06 Spr. and just about every other cartridge above the .243/6mm class, most of the time. The 30-06 Spr. is usually a few hundred feet per second faster then the 308 Win. so it shoots flatter and hits a little harder.