Comments on: Big-Bore Ballistics: Are Muzzle Energy Calculations Useless Information?

By: calinb

calinb — Tue, 21 Aug 2012 05:23:34 +0000

Cymond says:
>If muzzle energy is such a bad metric, then what do
>you propose? Velocity? Bullet diameter? Bullet
>weight? Bullet design? Any one factor, without
>the others, leads to obvious nonsense.

Yes–all of the above!

As long as we must calculate “knockdown power,” I like the WAVE formula discussed in the Mel Tappan classic, “Survival Guns.”

W x A x V x E

weight (more correctly, mass) x caliber cross sectional area x velocity x bullet efficiency

Bullet efficiency is 1.0 for a non-expanding bullet like FMJ and as high as 1.25 for a good expanding bullet.

Note that this metric is proportional to the square of the caliber (pi x radius ^2) This seems to be a better predictor of killing power than energy, which is proportional to the square of the bullet speed (velocity).

There are other similar formulas but WAVE is easy to remember.

By: Corrina Peterson

Corrina Peterson — Tue, 31 Jul 2012 13:29:43 +0000

Great discussion points Cymond – Thank you for taking the time to post the comment. It seems to me that the ‘perfect cartridge’ depends heavily on what it is you plan to do with it. And, as you noted, relying on any one of the factors, without considering the others, may not be the best way to choose an effective load for your purposes. Someone who understands the factors noted in your comment, and in Prasac’s book, will be better able to choose the best ammunition for their needs.
Thanks again for posting, and for reading the Books blog!
Corrina

By: Cymond

Cymond — Mon, 30 Jul 2012 21:28:49 +0000

As Peterson shows above, energy alone is a poor indication of effectiveness. However, it is the best way to compare similar loads. How do we choose between a .30cal 110grn bullet at 2700 fps and a .30cal 124grn bullet at 2400 fps?

If muzzle energy is such a bad metric, then what do you propose? Velocity? Bullet diameter? Bullet weight? Bullet design? Any one factor, without the others, leads to obvious nonsense.

It’s a well known fact that .223 Rem is widely used for coyotes. Would anyone recommend 22lr for that role? It’s the same caliber and weight as .223; only its energy/velocity is different. Deer are taken with .357 Rem Mag, but would anyone recommend .38 spcl target loads for the same role? I mean, they fire the exact same bullet, so they should be equally capable, right? The only difference is their velocity and their energy as it relates to velocity. Caliber and weight alone are not enough.

Is a bigger bullet better? Generally yes, but it’s a little complicated. Increasing bullet size without increasing weight means a large round-nose bullet with a poor ballistic coefficient and poor penetration in the target. Maintaining sufficient penetration requires either increasing velocity (same weight) or increasing weight (same velocity). Either solution means increased muzzle energy (and recoil).

Characteristics of a perfect cartridge:
a large caliber to damage as much tissue as possible
a heavy bullet for deep penetration
a high ballistic coefficient for long range
a high velocity for range and penetration

A cartridge like .50 BMG would satisfy all of those requirements, but it’s not exactly practical to drag through the field.

Is energy everything? No, it doesn’t account for everything but at least it considers multiple factors. That’s better than simply looking at a single factor. If someone has a better metric, please provide it.