As velocity increase, esp. in the smaller calibers, the greater the effect of sectional density and premium bullet design (partitions, A-Frames, Xs). As both velocity decrease and bore size increases, both sectional density and design decrease in importance. Once bore size reaches a certain point (over, say, 9.3mm), increased velocity may actually be a net negative, and bullet design is less and less important.
Thus, a heavy, large diameter projectile (say, a .458 diameter slug of 400 grains and standard design) will penetration further and more easily at a slow velocity (say, 1500 fps) than will a smaller, lighter, but roughly equivalent SD projectile at even twice the velocity (say, .308 caliber 220 grs. at 3,000 fps, for comparison purposes), unless the lesser caliber uses a premium grade bullet.
Real world comparison on similar ballistics:
405 gr. SP .45-70 fired at roughly 1400 FPS factory load
vs.
180 gr. SP .30-06 fired at roughly 2800 FPS factory load
Both classic big game cartridges and loads. Which will penetration further without the use of premium bullets?
So, small and fast, and premium, can go the distance through game, but big, and slow, regardless, often does the same.
