Bullets with better BCs can deliver flatter trajectories and faster impact velocities. (Photo by Richard Mann)
March 23, 2020
By Richard Mann
With all the attention given to shooting at distance, ballistic coefficient (BC) gets talked about a lot. It seems like there’s a race between ammo companies to see who can create a hunting bullet with the best BC. The reality is that for many hunters, BC is not that important. However, many have fallen victim to this need for speed, and practically speaking, speed is all that BC represents.
Let me explain. A bullet’s BC is a number generated by a mathematical formula that reflects the projectile’s estimated ability to overcome air resistance in flight. The larger the number, the less susceptible the bullet is to drag imposed by the atmosphere. Ballistic coefficient has very little to do with a bullet’s ability to damage tissue or kill an animal; it mostly relates to flight characteristics. Its relation to bullet speed is in time of flight. If two bullets leave the muzzle at the same velocity, the one with the best BC will get to the target sooner. It will lose less velocity to air resistance during flight, and because of its faster flight time, gravity and wind will have less time to act upon it.
To illustrate this let’s look at the external ballistics of two bullets I use in a wildcat cartridge I created and call the 2Fity Hillbilly. Also known as the .25 Creedmoor, it’s nothing more than a 6.5 Creedmoor necked down to accept a .257-caliber bullet.
The first bullet is a 117-grain Hornady InterLock RN (round-nose). It has a BC of .243, and I can push it to 3,020 fps from a 24-inch barrel. The other is the polymer-tip 110-grain Hornady ELD-X, which has a BC of .465. It’ll do 3,100 fps out of the same rifle. For comparison sake, we’ll give both bullets a muzzle velocity of 3,000 fps.
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With a 100-yard zero, at 300 yards the InterLock round-nose bullet will drop 14 inches and the ELD-X bullet will drop 11. That’s only 3 inches of difference. If both loads are zeroed for a maximum point-blank range—a range where the path of the bullet is never more than 3 inches above or below the line of sight—the difference in the distance where the bullet drops below this “window” is only 25 yards. With these parameters, maximum point-blank range is 275 yards for the InterLock and 300 for the ELD-X. Considering most hunters shoot big-game animals at much closer distances, this difference is of little consequence.
Ballistic coefficient is tied to bullet shape: Streamlined bullets such as the Hornady ELD-X have higher BCs than round-nose designs such as the Hornady InterLock RN. (Photo by Richard Mann SPECS
Hornady ELD-X
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.257-caliber, 110 grains BC: .465 Hornady InterLock RN
.257-caliber, 117 grains BC: .243 The author loads both the 110-grain ELD-X and 117-grain InterLock RN in his 2Fity Hillbilly wildcat. With a muzzle velocity of 3,000 fps, there’s not much difference in trajectory between the two bullets at 300 yards, but the ELD-X drifts 7 inches less in a 10-mph crosswind. (Photo by Richard Mann The 110-grain ELD-X has a slightly better BC than the 110-grain Nosler AccuBond (left), but at ranges less than 500 yards the difference isn’t enough to matter to hunters. (Photo by Richard Mann SPECS
Nolser AccuBond
Hornady ELD-X
But there’s more to the story than trajectory. Bullets with better BCs are more resistant to crosswinds. In a 10-mph, 90-degree wind, the InterLock bullet will drift 13 inches at 300 yards. That’s enough to turn a double-lung shot into a gut shot. The ELD-X bullet will drift only 6 inches. That’s a substantial difference that could matter a great deal if you’re shooting at a mid-range distance in windy conditions.
Granted, the above is an extreme comparison. When deciding between modern hunting bullets, most often the difference in BC is minimal. Comparing bullets with BCs of .465 and .400 at the same 3,000 fps velocity, the difference in drop at 300 yards is less than .5 inch, and the difference in wind drift is only about 1 inch.
From a practical standpoint, BC only really matters beyond maximum point-blank range. With modern high-velocity cartridges this is generally in excess of 300 yards. Comparing the .257-caliber InterLock and ELD-X at 500 yards, we see a difference in drop of 20 inches and a difference in wind drift of 24 inches. That’s considerable, and it’s all due to time of flight. It takes the round-nose bullet .74 second to travel 500 yards, but the ELD-X gets there in .60 second. Gravity and wind have .14 second longer to pull and push on the InterLock bullet. However, with the bullets we compared above that have BCs of .465 and .400, there’s only a 3-inch difference in trajectory and wind drift at 500 yards. The 16 percent difference in BC has only a marginal impact on external ballistics, because the difference in time of flight to 500 yards is only .02 second.
So, when does BC matter? Bullets with better BCs can deliver flatter trajectories and faster impact velocities. Both are good things for hunters, but to matter much at all the difference in BC and the distance to the target must be extreme.
