bbtiheadBallistics By the Inch — BBTI — is a website that does something we really like: tests and develops actual data about basic firearms facts. Like some of the other sites we’ve linked to over the last year-plus, it’s a myth-buster and a fact-finder. We do like that.

Some of these things have been extensively tested in the past, but three problems exist with these historical tests. First, the instrumentation available today tends to be more accurate than that available in the 20th or 19th Century, thanks to the computer and microprocessor revolution.

But the two other problems usually mean that those tests that do exist often are not on the net. One, perhaps they were done by government authorities that normally publicize data, but executed and recorded long before the internet’s event horizon of circa 1995. That means that they are only likely to be archived to the net if the agency cares enough to go back through its paper or microfiche archives and do so.

And two, perhaps they were done by some entity that did not care to put the information in the public sphere. Most foreign governments don’t, and companies conducting proprietary testing don’t.

BBTI’s Jim Kasper, Jim Downey and gang explain that these are only data points, and like any tests, BBTI’s have their bounds and constraints:

As we’ve noted previously, we have no illusions that our data is comprehensive.  It is meant to be indicative – giving an indication to the general relationships between barrel length and velocity, or the effect of a cylinder gap.  It would be impossible (for us, at least) to test all the different ammunition types available, or all the different firearms – particularly so when manufacturers of ammunition and firearms are constantly tweaking and improving their products.  So use the data here to get an idea of what to expect, and perhaps as a jumping-off point for your own research.

via BBTI – Ballistics by the Inch :: Home.

Screen shot 2013-04-07 at 10.24.53 AMExamples of the phenomena the site has examined include the effect of the cylinder-barrel gap on revolver velocity, the effect of shorter barrels on handgun velocities (starting with a long barrel and cutting it down), and comparisons of revolver velocities to equivalent-length, uninterrupted pistol barrels.

This is good data, it’s documented, it’s free, and it’s on the net. So what’s not to like? Well, apparently some people bitch about this or that. They bitch because he hasn’t tested Glocks (that’s coming). They bitch because they don’t understand the data. They bitch because… well, their psychologists could probably tell you. It’s data. It’s good. It’s free. What’s to bitch?

But with that said, we do have one quibble. In any aerodynamic or real-world ballistic experiment, you don’t have really comparable data unless you correct for atmospherics. This is usually done by correcting the data to an International Standard Atmosphere (ISA). The calculations are simple arithmetic, but you have to record the altitude, ambient pressure, and ambient temperature so that data can be normalized to an ISA (altitude Mean Sea Level, pressure 29.92 in/hg, temperature 59F). It’s possible they are doing this. This blog post, for instance, notes that they’re recording ambient temperature back in 2008. And this .pdf shows that they were thinking about pressure, but not pressure, when they originally conceived the tests. And there’s no question that they now how —  Kasper’s a physicist, after all (and every drag racer figures this out — it’s not rocket surgery). It would be nice if they noted whether these are ISA value data, or provided us the ambient atmospherics so one of us readers could make the calcs.

But that’s our only quibble. Lots of information there, and more promised this spring.

This entry was posted in Weapons Education, Weapons Technology, Weapons Website of the Week, Weapons Website of the Week on by Hognose.

About Hognose

Former Special Forces 11B2S, later 18B, weapons man. (Also served in intelligence and operations jobs in SF).

2 thoughts on “Wednesday Weapons Website of the Week: BBTI

Jim Downey

Thanks for the recognition!

Your quibble is a fair one, and as you note we originally did start recording ambient temp (with the altitude of the site known, and barometric pressure data available for any given day), but determined that whatever effect those factors may have had were lost in the noise of the other data (as seen in the variation of the benchmark test gun/ammo recordings). Since we were only shooting over a pair of chronos set about 15′ from the muzzle, there really wasn’t a lot of time for these factors to have much of an effect.

So, we stopped, deciding that it was just a confusing element for the tests – there is a danger in pretending that our data is more accurate than it actually is. The margin of error on our sample size (typically three shots, fired over two chronos) is just too great.

Just thought I’d share our thinking on this point.


Jim D.

Hognose Post author

Good enough. I’ve seen the difference atmospherics can make to things like runway length calcs, or jumpmaster calculations. Given the higher velocities and the Reynolds numbers you’re dealing with on a bullet, you’re probably right that it just creates a false illusion of greater precision that possible.

Funny how people automagically assume that a few digits across the decimal point means the measurement’s gotta be good. Like the way people say “12:47” instead of “quarter to one” since the advent of digital watches, but the precision display of the watch doesn’t mean it’s set right.