The Heavy Bullet Advantage

High Ballistic Coefficients Mean More Hits at Long Range

It seems that the latest rage these days is to find as light a .22 bullet as possible and then stoke it up to fly as fast as possible.  The new 40-grain Nosler ballistic bullet has a huge following.  PD shooters especially love this little bullet, since it is easily launched at hyper-velocities, even in the modest .223 Remington.  Flyweight bullets also seem to be popular in 6mm bore.  To be sure, a prairie dog hit at moderate range disappears most spectacularly when hit with a lot of velocity.  But shooters who think these bullets give them increased range over heavy bullets are sadly mistaken.  One need only look to target shooters to see the folly in selecting lightweight bullets.

Long-range target shooters very carefully choose their rifles, optics, loads, and bullets.  Like a lot of varmint hunters, they know what actions to choose, what scopes to use, and how to work up a load.  When it comes to bullet selection, however, target shooters leave most varmint hunters in the dust.  Generally, target shooters choose a fairly heavy bullet for the caliber they shoot; often, the bullet is the heaviest for the caliber.  For example, target shooters will often select bullets 190 grains and heavier for a .30 caliber rifle – you will never see them selecting a 150 grain load or even a faster 130 grain load.  Compare that philosophy to the current light-bullet trend in .22 centerfire rifles; 40-grain bullets at hyper-velocities are the norm.  Even military competitive shooters who shoot M-16s use heavy bullets.  The reason is simple: heavy bullets drift less in the wind.  There is more to the story than just the wind, but let’s cover the wind drift story first.

Launching a 40 grain Nosler BT at 4000 fps is no great feat in a .220 Swift; neither is it difficult to get a 75 grain Hornady A-Max up to 3200 fps.  (But you will need a fast-twist barrel to stabilize the bullet – see the sidebar on Shilen barrels for more details.)  At first glance, most shooters would guess that the lighter pill would shoot flatter but perhaps give up a bit in the wind drift contest.  Well…would you believe that at 500 yards the trajectories are almost identical?  More importantly, the heavier bullet’s rate of drop at 500 yards is ten percent less than the lighter bullet.  Wind drift is even more telling…at said 500 yards, the 40 grain bullet drifts 32 inches in the standard gunwriter’s wind (10 mph crosswind).  The 75-grain A-Max drifts a little over half as much – only 18 inches!  Sportsfans, that is a huge difference.  After all, even if the trajectory was not as flat with the heavy bullet, rangefinders can pinpoint the range and target scopes can move the reticle, but it is mighty tough to correctly guess the wind.

Table 1 – Trajectory comparison of a 40 gr Nosler BT launched at 4000 fps versus a 75 gr Hornady Amax with a muzzle velocity of 3200.  Trajectories use a 300 yard zero in standard conditions.

Table 2 – Wind drift of the same loads.  Even though the 75 grain bullet starts out 800 fps slower, it drifts incredibly less than the 40 grain bullet.

Table 3 – Trajectory of both the 40 gr Nosler BT at 4000 fps and the Hornady 75 gr AMax at 3200 fps, zeroed at 300 yards in standard conditions, but then shot in a temperature 30 degrees cooler.  While not as large an advantage as wind drift, the Hornady bullet, due to its higher ballistic coefficient, experiences less of a trajectory change when weather conditions differ from those used to zero.

To illustrate just how important the difference can be, suppose we are going to try and connect on a prairie dog at 340 yards.  The wind is blowing left to right at 12 mph, but we estimate it as 10 mph.  In a 10 mph wind, the 40 grain bullet drifts 13 inches, or 1.3 inches per mph of wind.  However, because we misestimated the wind (it was really blowing at 12 mph), the actual drift is closer to 15.6 inches.  Our error is 3 inches, so even if we are able to hold perfectly for the 13 inch estimated wind drift, our bullet sails almost 3 inches from the pasture poodle, which continues to munch grass.

On the other hand, the 75 grain Hornady V-Max at 3200 fps will only drift 7.75 inches in a 10 mph wind, or .78 inches per mph of wind.  A mistake of 2 mph results in an error of only 1.5 inches, clearly less.  And don’t forget, the actual bullet drift of 8.2 inches is a lot easier to estimate than 15.6 inches.  As you can see, wind drift presents far less of a problem for the 75 grain V-Max.  The reason?  You probably already know: a high ballistic coefficient.

It is often written that gravity is the great enemy of bullet flight; if we had less of it, bullets would shoot flatter.  That concept is flawed, for it is not gravity that hurts bullet flight, but air resistance.  Air resistance slows down a bullet’s time of flight.  Think about it this way: suppose you had two identically chambered rifles.  You are shooting both at sea level, but one bullet is shot just below the surface of the water.  In other words, one bullet flies through air while the other flies through water.  The effect of gravity is the same for each bullet.  Any guesses as to which one travels farther?  Of course it is the bullet travelling through air, not water.  But it is not due to gravity – it is due to the greater resistance of water slowing the bullet and causing it to travel less distance.  Another way to look at this is following riddle… “Suppose you held a rock in one hand and in the other hand held a rifle perfectly parallel to the earth’s surface.  If you then dropped the rock the instant the trigger broke, which would hit first?”  The answer: they both hit the ground the same time.  Of course, in the time it takes the rock to fall the bullet has traveled a great distance.  The exact distance the bullet travels is a function of muzzle velocity and ballistic coefficient.

Without going into the boring math details, ballistic coefficient is a numerical method expressing how efficiently a bullet slices through air.  A sharp pointed nose, a high sectional density, and a boattail base all contribute to a high ballistic coefficient.  It is easy to understand why a pointed nose is important; the boattail perhaps a little less obvious.  As a bullet flies through the air, it creates a slight vacuum behind it.  A boattail shape reduces the amount of vacuum generated.  Sectional density is the ratio of the weight of the bullet in pounds and the diameter in inches.  The importance of this is easy to appreciate; a heavy object is slowed less than a lighter one.  Therefore, all else equal, a heavy bullet will shed velocity slower than a lighter bullet.  But, for most varmint hunting ranges, a lighter bullet does indeed shoot flatter.

But there is more to the story than just trajectory.  With the wonderful variety of rangefinders available today, a flat trajectory is less important than it used to be.  Today, we can range to a target and then either hold over using a special reticle or crank the target adjustment knobs.  What we must still “guess” is the wind velocity or speed.  There are some handy devices that will measure wind.  Fifteen years ago I paid $50 (a lot of money for an Army lieutenant) for my first hand-held anemometer, or wind speed gauge.  It worked okay, but was bulky.  My second device was handier; it consisted of a tube with a small plastic ball.  As you held the device, the ball rose to indicate wind speed.  My latest solution to the problem is a Kestrel wind speed gauge.  It is lightweight and accurate.  What it does not do is indicate wind direction, but I use a cleaning patch tied to my rifle muzzle with a six inch section of thread to do that.  But there remains two significant problems: the wind speed can change, or it can be different out where your intended quarry stands.  Knowing how to read mirage can help quite a bit, but judging wind velocity remains a challenge.  And since wind remains so indeterminate, it is best to use bullets with as high a ballistic coefficient as possible. 

No serious big game hunter or long range target shooter would ever select a .30 caliber 110 grain bullet, even if it had the terminal properties desired, for the wind drift, as well as the trajectory, is terrible.  The same goes for lightweight .22 bullets.  If you are a very serious shooter, you may know all of this.  But you should also know this: bullets with a high ballistic coefficient are less affected by changes in temperature.  Suppose we are shooting 40 grain Nosler Ballistic Tips at 4000 fps.  We have a scope with target knobs, so we shoot at various distances so that we know how much to “click” at various ranges.  We zero in 70 degrees when the barometric pressure is 29.5 inches.  We travel to our hunting area, where the temperature is 40 degrees and the barometric pressure is 30.1 inches.  At 500 yards, these new conditions will cause the bullet to strike 2.7 inches low at 500 yards, 6 inches at 600 yards, and 12.2 inches low at 700 yards!  That’s right, a mere 30 degree temperature change combined with a .6 inch change in barometric pressure makes it tough to connect on a prairie dog at 500 yards and virtually guarantees a miss at longer ranges (not that it is easy without these complications).

As you can imagine, the 75-grain Hornady V-Max turns in a markedly improved performance.  At 500 yards, the bullet strikes 1.4 inches low, 2.7 inches low at 600 yards, and at 700 yards strikes only 4.9 inches lower in the same cooler temperature and higher barometric pressure.  In other words, the trajectory predictability of the heavier bullet, and consequently its “hittability,” are greatly increased.  The reason is simple...bullets with higher ballistic coefficients slice through air more efficiently, and are thus less affected by changes in atmospheric conditions. 

It is easy to forget that most .224 bullets have very low ballistic coefficients.  A 40-grain Nosler Ballistic Tip has a ballistic coefficient of only .221.  Compare that with the 110-grain .30 caliber Speer spire point; it has a BC of .273!  Or, consider this: the 180 grain Hornady roundnose, a true “round-nosed” bullet and consequently one with a very low ballistic coefficient, has a BC of .241, even higher than the 40 grain Nosler BT!  Granted, the 40 grain Nosler is launched with a much higher velocity than the roundnose bullet, but the velocity of a 110 grain .30 caliber bullet approaches that of the light .224 bullet, yet no one would consider this a combination a long range proposition.

I have no axe to grind with those who wish to use lightweight bullets; Steve Timm, who has killed more varmints than I ever will, loves ‘em.  But spectacular kills at moderate ranges do not translate to increased performance at longer ranges.  If you don’t believe the ballistics I quoted, go out and shoot for yourself at long range.  After all, that is what I did that led me to the discovery in the first place.  You see, using a very accurate .220 Swift firing 55 grain bullets at 3700 fps, I found it was actually far more difficult to hit small targets at ultra long range than when using a less accurate 7mm Remington Mag firing 150 grain bullets at 2900 fps.  To be sure, the Swift clumped the lighter pills in a tight group...problem was, the groups moved with the wind and the thermometer.  In the winter, when the temperature fell as much as 20 degrees below zero, the bullets would impact as much as two feet low!  As you might have read in previous stories, that Swift now sports a Shilen stainless barrel with a fast twist that shoots 75 grain Hornady and 77 grain Sierra bullets just as accurate as the lighter ones – but with only half the drop difference when the temperature falls.

For long range shooting, this is just the ticket for me.  A 75 grain Hornady A-Max launched at 3200 fps has a trajectory almost identical to the 7mm STW, a cartridge that has performed quite well for me at long range.  Wind drift and trajectory are just about the same, but recoil is far less.  Best of all, this combination lets me shoot varmints with a rifle that has exactly the same trajectory as one of my choice hunting rifles.  Wind drift and holdover lessons learned while shooting PDs make long range hits at big game just that much easier.  And that just might be biggest advantage to shooting .224 bullets with a high ballistic coefficient.