Understanding ballistics

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The “Big Book of Ballistics,” By Philip P. Massaro and published in 2017 by Gun Digest Books helps the reader understand ballistics. Today we continue to discuss seating depth, spin drift and more from the book.

Seating depth

Here is an area where my reloading buddies have been working on since we started assembling rifle cartridges. How deep should a reloader seat the bullet in the cartridge?

This is an important part of the reloading game. The shooter wants the bullet to sit just off the beginning of the barrel. Excessive pressure can be realized, if the bullet touches the lands and groves of the barrel, which is the beginning of the barrel.

This has been drilled into my mind for years and it is simply a fact. However, a series of seating depth tests, conducted by Massaro, explains the reason to experiment with this part of reloading.

He started with a cartridge length of 2.800 inches, this included the cartridge case, primer installed, loaded with powder and a bullet inserted into the open end of the case. This gave him a velocity of 2,638 feet per second and a five-shot group at 300 yards of 3 inches.

He then increased the cartridge length by .005 inches, so we are talking 2.805, velocity 2,644 and five-shot group of 5.25 inches. Then a length of 2.810, velocity of 2,650 and grouping of 4 inches. The test continued until he found the sweet spot of a length of 2.825, velocity of 2,644 and a five-shot group of 2 inches.

He went out to 2.830 and 2.835, but signs of excessive pressure began to show with the longest cartridge. The test was conducted again, with similar outcomes.

This test demonstrates the proper barrel harmonics for this particular rifle, powder and bullet combination.

Other chapters

The other various chapters include “The Projectile,” “The Ignition System,” “The Barrel,” “Exterior Ballistics,” Bullet Stability and Spin Drift,” “Wind Deflection,” and several more.

Spin Drift

This chapter caught my attention because most of us don’t think about this force on a bullet. When a rifle has a right-hand twist, a bullet will drift to the right. This is noticeable to long-range shooting, say when shooting 1,000 yards, but it is still a force on the bullet.

Second read

There is much more to this book than we have been able to cover in this column. My eyes have passed over each page, but it is time to begin again and read it one more time. Plus, “Big Book of Ballistics” will be a go-to reference book for my reloading buddies and me.

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