Home Forums Hunting & Shooting Hunting Rifles The .270

Maybe it will, maybe it won't. Once a bullet enters tissue, sectional density changes, unless, perhaps, if you're using a monolithic solid.

Bullets tend to deform and they tend to shed mass when they pass through tissue resulting in changes in the immediate sectional density. The typical bullet that exits the other side of a game animal, if it mushroomed, and even if it has the same weight as when it entered, doesn't have the same section density coming out as it did when it went in. That's how a study of terminal ballistics sets the notion that, for instance, a 165 grain 7mm bullet launched at a higher speed than a 145 grain 7mm bullet launched at lower speed will always out penetrate the lighter bullet on its ear. It's just not always the case.

Studies have shown that in 'some' cases a lighter bullet at a slightly higher velocity can penetrate deeper and retain more of its mass than the same bullet with a higher initial sectional density and at a slightly lower velocity. Some have shown that a bullet designed to retain mass that's lighter than one that isn't as well designed to retain mass may outperform he heavier bullet with respect to penetration while generating a similar wound cavity. But these things aren't reliable rules of thumb. In the work "The Mechanics of Terminal Ballistics" tests showed a 145 gr Speer Grand Slam out of a 7mm-08 at 2735 fps can out penetrate a 160 gr Swift A Frame out of a 7mm RM at 2930 fps, even with the former shedding more mass than the latter, apparently because the former expanded less than the latter resulting in a higher immediate sectional density. Bullet shape, construction and velocity generally are the 1-2-3 most important factors in penetration, though velocity helps in breaking things.

These discussions surrounding external ballistics are interesting. And if target shooting is all there is to the issue at hand, maybe going beyond external ballistics isn't necessary. But with respect to effectiveness on game, no proper conclusion can be had without an understanding of terminal ballistics.