Ballistics a brief overview

Ballistics . . . The word sounds impressive and most assume it deals with a bullet in flight. That assumption is only partially correct. There are three separate fields of study within the realm of ballistics. They are (in sequential order) "Internal" Ballistics, "External" Ballistics, and "Terminal" or "Wound" Ballistics.

Internal Ballistics looks at powder burning rates, pressure curves, bullet to bore fit and friction, barrel vibrations, primer ignition and even touches on rifling shape, groove depth, and twist rates of the rifling. Pretty heady stuff that I care little about, beyond knowing that a reloading manual publishes loads that are safe and have been proven to be so.

External Ballistics deals with the bullet in flight, it touches on the crown of the barrel (where free flight begins) and looks at bullet nose impact point. The shape of the bullet, the rate at which a bullet spins along the axis of its flight path, the launch velocity, and how well the bullet retains that velocity as it travels through the air. This is where we get things like B.C. (Ballistic Coefficient) and why the current fad of "boatail" bullets.

Terminal Ballistics (now called wound ballistics) studies what the bullet does from the time it impacts the target until it stops forward motion, and looks at the effects said impact has on the target. This is where we look at jacket thickness, and material, bullet hardness, and how well a bullet stays in one piece after hitting its target, and at what velocity the impact occurred. We also look at temporary or stretch, and permanent wound cavities.

How does all this work? Easy. Lets say you want to go hunting. You decide to take a 30 caliber magnum centerfire rifle and you are going to hunt deer. You go to the store to buy ammo for your gun and have to stop and think...what bullet weight, and how tough of a bullet do I need...you decide on 180 grain boatail because they give you the flattest trajectory (external ballistics) and reliably harvest game out to the horizon (terminal ballistics), besides you tried them a couple years ago and your rifle shot them really well (internal and external ballistics)

Something you may want to look into if you are considering loading your own ammo is the study of not only the external ballistics, but the terminal ballistics. These two will help you load and place the right bullet for the job into the target.

I settled on cast bullets for 99% of my hunting and shooting. I shoot lower velocity (under 3,000 fps) rounds, and prefer not to risk a bullet opening too quickly and limiting penetration so much that the shot only wounds. This happens with very fast opening bullets reaching a target animal while traveling faster than designed to. (Too high of an impact velocity will not reliably nor quickly kill an animal) With cast bullets that is just not a problem.