Riflehunter,
Bullet diameter does matter--but a .338 bullet is only .03 larger in diameter than a .308 bullet, about the same as a slightly thicker than average human fingernail.
What really matters is expanded diameter, since it creates a larger wound channel, whether temporary or permanent.
This is why a few years ago I measured the diameter of a bunch of expanded bullets recovered from big game in different calibers. As it turned out, there was basically ZERO measurable difference between the expanded diameters of .308 and .338 bullets, regardless of weight and make. There was a difference starting with .358 diameter bullets, and somewhat more with 9.3mm and .375 bullets.
Yeah, the high sectional density of heavier .338 bullets can result in deeper penetration. But I used a .338 Winchester Magnum from 1988 to 1999 on a pile of big game animals from Alaska to Africa, ranging up to around 1500 pounds in weight. The big thing I noticed after all that was that lighter bullets from 200-225 grains tended to kill quicker than bullets over 225 grains, no matter the brand. Velocity plays a role as well.
You'll find more of the details of my bullet-diameter investigation in Chapter 41 of my Big Book of Gun Gack II, "Opinions of Killing Power." Oh, and the trajectory of a 250-grain spitzer from the 9.3x62 at 2650-2700 fps (just about the same as 250's in the .338 Winchester Magnum) is basically the same as the .30-06 with 180's--and it's no big trick to shoot big game out to 400+ yards.
Mule Deer, if .338 is 10% bigger than .308 and .358 and 9.3 is 10% bigger than .338, then it wouldn't be diameter that makes a difference. If using mono's then construction would be same. The shape of mono's would be similar. What would be the factor that would make .358 superior to .338 in these circumstances when .338 has better SD with same weight bullets?
