Ammunition performance (as I understand it)
This is a discussion on Ammunition performance (as I understand it) within the Defensive Ammunition & Ballistics forums, part of the Defensive Carry Discussions category; Some thoughts based on my webcrawling for data about choosing defensive ammunition.
1. The reason most defensive ammunition performs similarly in tests is that most ...
Post By Madcap_Magician
Post By NYMike
May 4th, 2012 12:17 PM
Ammunition performance (as I understand it)
Some thoughts based on my webcrawling for data about choosing defensive ammunition.
1. The reason most defensive ammunition performs similarly in tests is that most common defensive ammunition is all designed around the FBI protocol ballistic gelatin test.
2. In general, bullets with a higher sectional density penetrate further. It's not as simple as which bullet is heaviest, as a 147-gr. 9mm bullet tends to penetrate further than a 185-gr. .45 ACP bullet. Sectional density determines how efficiently a bullet can penetrate an object (including air), and it is expressed by the formula SD=M/(CSA), where SD= Sectional Density, M= Mass, and CSA= Cross-sectional area. The sectional density of the 147-gr. 9mm round is .167, whereas the sectional density of a 185-gr. .45 ACP is .131.
The expansion profile of a modern JHP design changes the sectional density of the bullet as it expands. That is, the sectional density of an unexpanded 9mm bullet is .167, but it decreases as the bullet expands, increasing the frontal surface area of the bullet and changing the SD equation calculation.
The calculation for frontal surface area of a bullet as it expands is much more complex, because modern JHPs do not expand in a perfect circular fashion but rather have 'petals' and jagged edges. I think this may be why solid copper bullets penetrate deeper than you would otherwise expect for their weight- the Barnes DPX bullet, when expanded, does not have the lead 'mushroom' of a traditional JHP that greatly increases frontal surface area of the expanding/expanded bullet, and the DPX retains most of its mass at the same diameter of the original bullet, with the expanding petals matching the overall diameter of a traditional JHP, but not the frontal surface area.
I do not have the math to calculate the effect of the shape of the bullet from the front. I.e. I think that a bullet with sharp edges toward the front will penetrate deeper than one that is flattened without sharp edges. This would be for the same reason that it's easy to stab yourself with a nail, but not with a penny, even if the mass and velocity are the same.
3. In general, for two bullets of the same design, the faster bullet will expand to a greater diameter in less time than the slower bullet.
This means that a faster bullet's sectional density will decrease faster than a slower bullet of the same design and weight. Extrapolating, I think that firing the same ammunition out of a short-barrel firearm is likely to produce slightly greater penetration and slightly less expansion than it would out of a service sidearm. I believe this is born out to a certain extent by anecdotal data until you start having serious differences in barrel length, i.e. pistol-caliber carbine v. pistol.
4. Relying on muzzle energy as a gauge of your defensive ammunition's effectiveness is inaccurate.
KE= Mass x Velocity^2, so faster bullets will have outsized kinetic energy compared to slower, heavier bullets, but the performance is likely not going to be all that different- again, a slight edge to the fast bullet in expansion, and a slight edge to the slow bullet in penetration.
Additionally, KE only matters insomuch as that energy is delivered to the target. The only way to ensure total delivery of the energy is to have the bullet stop inside the target.
Even if kinetic energy were actually important, to put it in perspective, the kinetic energy of a .44 magnum 240-gr. Hydra-Shok at 1380 fps from a 6" barrel is 1015 ft/lbs, or 1380 joules. To put that number in perspective, the energy of solar radiation hitting a square meter of earth over one second is about 1000 joules. Another way to look at is that the energy from a .44 magnum is about sufficient to heat half a bottle of water by less than two degrees Celsius.
May 4th, 2012 01:19 PM
I think you're over-analyzing the crap out of it! (I'm an engineer, and I tend to do that, too).
Pick a caliber, get some Ranger T's, HST's, or Gold Dots, and fuggedaboudit.
(P.S. - I'll be the first to say it: "Shot placement is King!")
May 4th, 2012 01:44 PM
It's not the size of the caliber but the skill of the operator.
May 4th, 2012 01:58 PM
in 1st place is accuracy and speed
in secocnd place is the caliber
-----you drive a car around town & on the highway at ~75mph ( most speed enough to keep up with traffic)
so you have basic, minimal driving skills and get in a paint swapping event every 5 to 8 years. thats average
if you have this level of skill with a gun than im thinking that on your person it will be 50/50 that in an
event it aids you vs not.
and the caliber of the car, just so it is reasonable in condition and power, is less important* in accident avoidance
than the skill of the driver. *the vast majority of the time
but those who have skills above average, like a race driver, not INDY, but good at the regionals--
you are the trained and alert person who carrying will be ever so much more be in your favor.
and those few who are the INDY 'drivers' may be the teachers, instructors for other teachers or just quietly
in the background with their skill cause it serves them, their needs.
one needs to think about all aspects of the gun and the enviornment we have it in,
but its a balance of all the aspects rather than one stand alone thing.
You plug 'em, I plant 'em
...kid can't read at 17 (Garcia/Hunter 1985)
Lack of preparation on your part does not necessarily constitute an emergency on mine
May 4th, 2012 02:04 PM
Ammunition performance data (on average) revolves around average circumstances and those willing to search and log all data available.
YOUR performance with the ammo you choose may or may not be added to the statistics, but that's only after you've become a statistic. Remember that. Keep yourself out of the data however you can. Your enemy is the only one who wants you to be confused. Perform to the best of your ability with what you have at the time. Supporting actors may get recognized, but they don't get the spotlight. Calculate surviving above all else. You can never second guess anything once your dead.
May 4th, 2012 03:55 PM
I'm digging into this data because I enjoy ballistics, not because I'm searching for a perfect caliber or bullet, folks.
May 4th, 2012 06:30 PM
Sam Rudolph, thanks for the enlightening thoughts and info in the thread. Discussions like this may be over-analyzing, but some of us enjoy that. For my 2 cents this is a fun read.
Sure, the best thing is to be prepared in every area, whether we're talking driving, CCW, camping or other. I may be well-trained as a driver, but I still like to think about different fuels, engine performance tire pressure and all the things that can make my vehicle (or weapon) perform best. Thanks again Sam.
May 4th, 2012 10:47 PM
All I need to see on a box is 230gr and .45acp.
(I'm just kidding around, not trying to start a caliber war)
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