**The 101 on practical ballistics**

*whole*lot more technical than that (a quick peek here gives you an idea), but this quickly moves into the realm of specialty. For the basics, rocket science is definitely

*not*required--just a little attention to detail.

__Trajectory__

*wind resistance*(drag), which is determined by the shape of the bullet, and

*gravity*, which is constant. These, along with the initial velocity of the bullet, can be used to calculate the bullet's

*trajectory*, or flight arc, to a degree of accuracy suitable for general-purpose shooting. This arc has the shape of a vertical parabola, and it is useful to the rifleman because it tells us where that bullet is going to be at given points along its flight path. We use the information in this curve to regulate our sights for a maximum "point-blank" range,

*within which we can essentially ignore the curve*while aiming.

__Maximum point-blank range (MPBR)__

*very*big deal. At sufficiently long distances, the problem becomes not so much how much you need to over-hold, but how accurate is your assessment of the distance to the target. For the hunter, misjudging a 350-yard shot as a 325-yard one (and that's

*easy*to do) might make the difference between a good hit in a deer's vital zone after breaking the shoulder, and one that hits below the vital zone, crippling the foreleg. This is not ethically acceptable!

So, we decide for ourselves the maximum distance from our exact point of aim that we are willing to let shots drift due to trajectory, and then regulate our sights so that the shot's arc stays within that tolerance for the maximum possible "point-blank" distance to target. The barrel is actually *elevated* slightly, such that the shot actually begins under the true line of sight, traveling *upwards *for a distance to our selected maximum ordinate (this would be the apex of the parabola) and only after that actually begins to *drop *relative to the line of sight. What we would look for is a trajectory that allows a maximum point-blank range as close as possible to our working maximum range--where only at the outside edge of our ability to place the shot, do we need to worry consciously about over-hold. (This is a compromise that we'll talk about more in a future section about selecting an appropriate cartridge.)

The maximum ordinate occurs

*above*the true line of sight at about 128 yards, and again

*below*the line of sight at 226 yards. This means that from the muzzle all the way out to 226 yards, we can hold in the exact center of our target and expect the bullet to hit within three inches of that point of aim, and this frees us up to focus on the nontrivial problem of our ability to

*hold accurately*under varying conditions. In short, MPBR is a practical way to make trajectory considerations as trivial as possible at common engagement ranges. Only at ranges that are

*way*out there, does one need to start consciously compensating for drop.

Incidentally, note the dramatic difference when we change the maximum ordinate to *four *inches, implying an 8-inch target size. MPBR is recalculated to 297 yards, with the "midrange trajectory" (maximum *positive *ordinate) at 141 yards. The table recalculates thus:

That is certainly significant--the MPBR with a four-inch ordinate is almost exactly the same as our maximum working distance. Is this then

*better*than using the three-inch ordinate? This will depend on your preferences. The penalty you pay with a larger maximum ordinate is that you may have more occasion to

*under*-hold at common shorter distances for precision shots, and that begins to defeat the purpose of zeroing the rifle at a maximum point-blank range.

Which is a nice segue into the key wrap-up thought about trajectory. Do not let the mathematical, theoretical aspect of all this become it's own *raison d'etre*. We look at MPBR as a rough *comparator *of trajectory between different cartridges, or different loadings within the same cartridge. (This will start to make more "real-world" sense as we discuss comparisons between cartridges.) Once you have settled on a cartridge and a loading, and have zeroed your rifle the way you want it, you should shift your focus to confirming for yourself, off a bench rest at known distances, just exactly what your shots ** are** doing at those ranges. Historically, published ballistics for factory-loaded cartridges can vary significantly due to very normal factors like temperature, variances in barrel length and other attributes of your particular rifle, etc. Do not trust the factory's published ballistics, which are often optimistic--

*see for yourself*.

**Next time...**

The next article in this series will discuss the other primary use of comparative ballistics: the even less-exact science of assessing whether the bullet has enough *power *to accomplish its task--not at the muzzle, but out there where it actually hits the target.

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