This is a two-part series about the book, “Big Book of Ballistics.”
Ballistics: The science or study of the motion of projectiles, such as bullets, shells and bombs. Also, the art or science of designing projectiles for maximum flight performance.
“Big Book of Ballistics,” By Philip P. Massaro and published in 2017 by Gun Digest Books has been taking up a considerable amount of my time lately. This book is big, indeed, at 8-inches by 11-inches and 335 pages crammed full of information.
It is the type of book to be used for reference for years into the future. It covers interior ballistics, exterior ballistics and terminal ballistics, plus a bunch of information in between
Most hunters know some of the basic information in the book, but Massaro covers a bunch of the info some hunters are a bit shy about discussing.
Headspace is an example under the broader title of The Cartridge Case. Defined as: The distance from the face of the locked bolt to a datum line or shoulder in the chamber that arrests the forward movement of the cartridge. Another definition: Headspace is the distance from the base of the cartridge case to the point on the cartridge case that prevents the cartridge from moving any farther forward in the chamber.
This sounds simple enough, but the concept is not being absorbed into my brain. Someone is going to need to demonstrate headspace to me in an actual rifle. Plus, how does it affect rifle accuracy?
Case capacity is discussed. This covers the amount of powder a cartridge case will hold. Remember, the goal of reloading rifle ammo is to find the best load for a specific rifle.
There is a chance to put so much powder into a .30-06 case which requires the powder to be compressed when seating the bullet. Massaro states when the powder is compressed, the grain structure of the powder runs the risk of being broken.
Although compressing powder in a cartridge case can be accomplished and still be safe, the powder in my reloaded .30-06 rounds are not compressed. There is no reason for me to even experiment with this much powder.
Rifle barrel harmonics is discussed, which cleared up an area which was confusing to me before. The barrel whips, torques and contorts when a shot is fired, so optimum accuracy is achieved when the harmonics are repeatable and aligned, so to speak.
Variables affecting barrel harmonics include the amount of powder used, the seating depth of the bullet and a couple of other items.
Next week: We will discuss seating depth, spin drift and more.