Why are there so many bullet weights for most cartridges? In .308 Win. you find bullets from 100 grains to 220 grains. Even the .224 Wthby. Mag. offers 32- to 80-grain bullets. Why?
The old rule of thumb: Use the lightest slugs for varmints (small critters) and heaviest for really big stuff. The basic reality was that heavier slugs retained more weight, thus offered more penetration. Today, things are more complicated. (Isn’t everything?)
No longer limited to standard cup-and-core bullets (soft lead core swaged into thin gilding metal jackets), we can find hard, controlled-expansion, deep-penetrating bullets in amazingly light weights. Monolithic all-copper or gilding-metal bullets such as the Barnes TTSX, Winchester Power Core 95/5, Nolser E-Tip and Hornady GMX retain so much mass after impact that they penetrate as deeply as old, considerably heavier cup-and-cores. Thick-jacketed, bonded-core and/or mechanically locked bullets such as Nosler Partition, Swift A-Frame and Winchester XP3 do much the same thing.
This means we can now choose lighter bullets to accomplish what the heaviest used to do. In the .270 Win., use a 130-grain monolithic bullet to penetrate as deep as (or deeper than) a traditional 150-grain. The right monolithic 130-grain .308 Win. projectile might penetrate deeper than a cup-and-core 180-grain in the same caliber.
But there are other advantages (and disadvantages) to lighter bullets. Given the same basic shape as heavier ones, they almost always fly flatter because they can be started faster. The heavies retain more energy farther downrange, but if you want minimal drop, shoot pointy light ones. Lighter slugs generate less recoil, too, so if you’re recoil-sensitive, light bullets are your friend. Just make sure they’re tough enough to stand up to impact velocities.
Another reason controlled-expansion (monolithic) bullets penetrate better than their weight suggests is because they don’t expand as much as soft lead. Mushrooming is good for increased wound area, bad for penetration. The flatter the bullet deforms on impact, the more it drags. A great compromise for penetration and radial tissue damage is expansion of 1.5 to 2X original diameter. Combine that with virtually no loss of mass and you’ve got the best of both worlds.
A final factor in choosing bullet weight involves wind drift. The heaviest slugs (of any given materials) are always the longest, and, given similar nose and tail shapes (long and sleek,) they have the highest ballistic coefficients (B.C.). This means they resist air drag, retain more energy downrange and deflect the least in wind. So while they’ll fall faster than lighter slugs, they’ll deflect less in the wind.
Regarding my feeling about bullet weights in the face of wind drift, consider this scenario: Out West, coyotes are often hunted in strong winds, so minimizing wind deflection is smart. Gravity is constant, so once you know your bullet’s speed and B.C., you can chart its drops and calibrate your scope sighting system to handle that. But judging wind is as much art as science. I try to minimize wind deflection by using the heaviest, highest B.C. bullet I can in my long-range coyote rifles. This means I probably shoot a 75-grain Hornady A-Max or Swift Scirocco in my .22-250 Ackley. At 3,350 fps, both drop a lot more at 400 yards than my 55-grain Nosler Ballistic Tips or Sierra BlitzKings at 3,800 fps, but they deflect much less in the wind. Because I can’t predict or even accurately measure wind speed, I increase my chance for hits with the heavy bullets over the light.
Light bullets shoot flatter than heavy bullets of the same caliber, but the high
B.C. of heavy projectiles ensures they retain more energy downrange and drift
least in wind. A stout, controlled-expansion light bullet can penetrate as well as
a much heavier one of softer construction. (Pictured: .264 Wthby. Mag. bullets.)