coylh
Member
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As a result of some discussions about bullet performance, I started collecting
published data on gelatin shoots. This was very interesting and I enjoyed doing
some simple statistics and playing around with Excel.
The natural inclination is to compare different cartridges or bullets, to find
out which ones are better. However, I began to be dissatisfied with some aspects
of using these gelatin tests in ranking loads.
I have along the way developed the suspicion that most gelatin results can't be
compared to each other with precision, and that the method I was using to rank
loads is flawed.
I've organized my complaints into sections. Most of this is quotes from
[url]www.firearmstactical.com:[/url] they come accross as very professional gelatin
shooters.
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Very few people publishing gelatin results document their data well. Often it's
not even stated what percentage of gelatin was used.
"When gelatin is not calibrated it’s impossible to determine the validity of the
data."
-- [url]http://www.firearmstactical.com/briefs9.htm[/url]
"... gelatin consistency varies greatly with temperature and how it was made.
The mandatory calibrating of gelatin is as fundamental to scientific method as
verifying the accuracy of a sensitive balance with a known weight."
-- [url]http://www.firearmstactical.com/streetstoppers.htm[/url]
"A good researcher/author will publish his ordnance gelatin calibration data
(BB velocity and penetration)."
--http://www.firearmstactical.com/briefs9.htm
"If two or more gelatin blocks are going to be lined-up end-to-end to capture
the entire wound path of the bullet under test, each and every gelatin block
must be calibrated ..."
-- [url]http://www.firearmstactical.com/tacticalbriefs/volume3/number2/article1.htm[/url]
It's rare to see calibration data listed and it's unheard of for testers to
list multiple calibration data when they use two blocks of gelatin, yet it's
common to see two blocks used when penetration is deep.
Calibration BB penetration can vary by 42%* even with the best testers, yet
no one is correcting for calibration penetration inconsistency except
firearmstactical (and they do so only sometimes).
* 2.91 - 4.13 inches [url]http://www.firearmstactical.com/briefs.htm[/url]
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"Clothed gelatin" test results use a variety of materials, thicknesses, and
number of layers. This complicates comparison. This however, may not be
unrealistic; people shot will be wearing a variety of clothing. Never the
less, it is in the spirit of gelatin testing to produce repeatable results,
and using different test methods complicates comparison.
"FBI Ammunition Test Protocols ... The gelatin block is covered with four
layers of clothing: one layer of cotton T-shirt material (48 threads per
inch); one layer of cotton shirt material (80 threads per inch); a 10 ounce
down comforter in a cambric shell cover (232 threads per inch); and one layer
of 13 ounce cotton denim (50 threads per inch)."
-- [url]http://www.firearmstactical.com/briefs26.htm[/url]
"... two layers of loosely layered denim."
-- [url]http://www.goldenloki.com/ammo/gel/tests.htm[/url]
"... covered by four layers of 16 ounce denim cloth."
-- [url]http://www.firearmstactical.com/briefs9.htm[/url]
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There are two basic measurements made in gelatin tests. One is the final
expanded diameter of the bullet. Unfortunately measuring this is more
difficult that it sounds:
"... effective expanded bullet diameter is difficult to estimate with
useful accuracy because the expanded periphery is inevitably irregular and
not easily related to the effective expanded diameter."
-- [url]http://www.firearmstactical.com/iwba.htm[/url]
Some bullets are so irregularly shaped that the tester provided two
measurements*: one of the lead core and another for the jacket.
* [url]http://www.firearmstactical.com/test_data/40sw/win40-180rsxt-g27.htm[/url]
In addition, different people measure the diameter with different techniques:
"... and measured for expansion by averaging its greatest diameter with
its least diameter."
-- [url]http://www.firearmstactical.com/briefs26.htm[/url]
"Recovered rounds were measured at multiple points and then averaged to
account for uneven expansion."
-- [url]http://www.goldenloki.com/ammo/gel/tests.htm[/url]
"... calculated on the basis of four cross-sectional measurements of each
bullet face."
-- Shooting Times 1997 June p52
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The other measurement is penetration. In otherwise similar bare gelatin
shoots where you would expect repeatable results, the penetration is
sometimes inconsistent, even though the values listed are averaged results.
5 shot average: .40 S&W Golden Saber 165grains@1022 = 14.8 inches of penetration and .65 caliber expansion -- [url]http://apollo.demigod.org/~zak/firearms/fbi-pistol.php[/url]
5 shot average: .40 S&W Golden Saber 165grains@1043 = 12.0 inches of penetration and .68 caliber expansion -- [url]http://www.firearmstactical.com/test_data/40sw/rem40-165gs-g27.htm[/url]
5 shot average: 9x19 Win Supreme SXT 147grains@921 = 17.6 inches of penetration and .50 caliber expansion -- [url]http://www.firearmstactical.com/test_data/9mm/win9-147ssxt-g26.htm[/url]
3 shot average: 9x19 Win Supreme SXT 147grains@912 = 13.5 inches of penetration and .53 caliber expansion -- Shooting Times 1997 June p52
5 shot average: .45 ACP Golden Saber 185grains@1037 = 14.4 inches of penetration and .72 caliber expansion -- [url]http://apollo.demigod.org/~zak/firearms/fbi-pistol.php[/url]
5 shot average: .45 ACP Golden Saber 185grains@1046 = 10.1 inches of penetration and .87 caliber expansion -- [url]http://apollo.demigod.org/~zak/firearms/fbi-pistol.php[/url]
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One of the units of measurement used to rank performance is Theoretical
Hole Volume (THV). That is, imagine that the bullet destroys a cylinder
shaped volume of tissue in the target that is as deep as the bullet penetrated,
and as wide as the bullet's final expanded diameter.
The penetration and expansion measurements which THV is derived from may
suffer from their own problems of measurement. However, even if these two
measurements were perfect, the formula's theoretical measurement differs
from reality in three ways:
a) A particular bullet doesn't crush the same amount of tissue throughout
the length of its wound track:
"As a bullet penetrates soft tissue, it loses velocity, and this affects
its 'effective diameter.' When the bullet first penetrates and expands, it
is moving so quickly that it crushes almost all soft tissue it comes into
direct contact with. However, as velocity begins to slow, soft tissue is then
able to stretch around the smooth outer edges of the mushroom-shaped lead
core shoulder to move out of the way. As the bullet slows further it plows
more and more tissue aside instead of crushing it.
Near the end of the wound track, the diameter of the permanent cavity might
be less than 60 percent of the expanded diameter of the bullet. The last few
inches of the wound track are the most important because this is where the
vital cardiovascular structures are located that you’re trying to damage."
--http://www.firearmstactical.com/briefs2.htm
b) Different bullet shapes inherently crush different amounts of tissue:
"A round nose FMJ bullet crushes a permanent cavity in soft tissue that
averages approximately 66 percent of the bullet’s diameter. Whereas the
blunt, non-aerodynamic shape of an expanded JHP bullet crushes a permanent
cavity that averages approximately 82 percent of the bullet’s expanded
diameter."
--http://www.firearmstactical.com/briefs23.htm
c) A bullet does not penetrate the target at its expanded diameter. There
is some distance, even if short, where the bullet is expanding.
These three factors make theorizing about the size of the permanent cavity
difficult. Besides, the value of gelatin is that you can measure real
results, not theoretical values. Why go to the significant trouble of
gelatin testing to obtain real, measureable results, only to turn around
and estimate in the actual ranking of performance. Why not just measure
the permanent cavity?
Sorry this has been so long, but I thought I would point out some aspects
of gelatin shooting that have left me with doubts about the whole process.