Ballistics by the inch

“How can I use your data?”

We get a fair number of questions to the BBTI email account ( ), which I try to answer as quickly as my time will allow. Most are about specific points in our data, or why we did this or that in our procedures (answers to most such can be found in our FAQ). But every once in a while a question comes along which pushes me to re-think things from another vantage point. The following is one such from “drglenn”, and I thought I would share it and my answer:

Found your website interesting, but I am uncertain how I can use this data reliably for me. Perhaps you can offer some guidance. Clearly, barrel length data can be used relatively to compare any single caliber/brand/bullet mass to itself. This is useful to see muzzle velocities/energy as a function of barrel length which might help the consumer in determining just how much more value they will get by purchasing a longer barreled firearm. What I found frustratingly non-useful is an inability to compare bullet mass to velocity/energy across brands – or even within a single brand – of stock ammo. This, no doubt, is a function of powder composition, cartridge air-space volume, and quantity of said powder. One might reasonably assume that, every other parameter being equal, a bullet with more mass, will have a lower muzzle velocity. One might also reasonably assume that since E=1/2mv^2, that velocity is much more significant than bullet mass in determining energy (i.e., all else being equal, if you could double the velocity, you would get 4x the energy, while doubling the mass will only yield twice the energy). Apparently, this useful bit of physics becomes completely useless as each manufacturer uses different powder formulations and quantities for their ammo. So, while I may be able to determine that, across the board, a certain mass bullet or higher, in a certain caliber, regardless of manufacturer, may be subsonic, it would be a crap-shoot in guessing which mass and which manufacturer should have the highest muzzle energy in a given barrel length.

Suggestions for best use of your data would be appreciated!

Sorry, I’m not quite sure what you’re asking. You’re correct that because of proprietary powder formulations, there’s no easy comparison between different manufacturers or even between different ‘lines’ of product from a given manufacturer. In fact, the situation is even much worse than you state, because the manufacturers are *constantly* tweaking their formulations in an effort to claim more of the market. And then there’s the whole matter of terminal ballistic performance depending on the actual bullet design and composition. Toss in the fact that firearms manufacturers are also constantly making minor alterations to their models and production methods, and yeah, it’s impossible to say with any certainty that this or that combination of gun and ammo will give a reliable result. In short, there is no “perfect” solution to the very complex problems of ballistics — one of the reasons why it has a long history of attracting some of the finest minds in physics.

But you can gain insight in what to expect within certain parameters using our data. You can see that while most semi-auto handgun ammunition performs best in a certain range of barrel lengths — usually from 3″ to 8″ –, that ‘magnum’ rounds intended primarily for revolvers will continue to gain velocity/energy over a much longer range of barrel lengths, and so is more suitable for a carbine. You can tell that most ammo formulated to be “low recoil” means that it has less overall velocity/energy, since you can’t break the laws of physics. You can see that some manufacturers may claim performance standards which aren’t supported by our tests, and some are right on the money. You can argue with your friends over a beer whether it is better to use a slow heavier bullet or a lighter one which goes much faster.

In short, our data is a tool for helping analysis and decision-making, nothing more. It’s certainly not perfect. It’s not even comprehensive within a given caliber/cartridge. And it is in some sense rendered obsolete each and every time the manufacturers tweak their production materials or methods. Which is why we always tell people to consider it indicative, not definitive. Use it if it makes sense for your needs, don’t if it doesn’t. And always – ALWAYS – know that testing your own ammo out of your specific gun is the only way to know for sure how it will perform.

Hope this helps.

Jim Downey

June 4, 2015 - Posted by | Data, Discussion., General Procedures | , , , , , , ,

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