Why Is There No Temporary Cavity For the Shotgun?

[Blastem]

I was looking at the image below and see that all the bullets have a temporary cavity yet the 12 ga.does not.

I first simply thought that the shotgun pellets were traveling slower than the others but then noticed that they are actually about 30% faster that 9mm.

In fact the temp. cavity on the 9mm is about 4x the diameter of the permanent cavity. For arguement's sake lets say that the shotgun temp cavity were only 3x the diameter of the permanent cavity - then that would seem to be a significant difference from the image below.

Could there be an error in the drawing that we have all been looking at and accepting as correct for all these years?

Your thoughts please.

Thanks in advance!

[chapperjoe]

my guess would be that each individual pellet isn't all that impressive given their shape?

[Gecko_764]

It looks like it may have something to do with the expansion of the bullet...although I could be (and probably am) wrong. Is it the energy of the bullet expanding/being dissipated outwards that causes the cavity?

[Zhukov]

The majority of the temporary cavity is caused by bullet deformation in tissue, ie. the hollowpoint opening up, the jacket fragmenting, etc.

No such phenomena with shotgun pellets.

[481]

I was looking at the image below and see that all the bullets have a temporary cavity yet the 12 ga.does not.

I first simply thought that the shotgun pellets were traveling slower than the others but then noticed that they are actually about 30% faster that 9mm.

In fact the temp. cavity on the 9mm is about 4x the diameter of the permanent cavity. For arguement's sake lets say that the shotgun temp cavity were only 3x the diameter of the permanent cavity - then that would seem to be a significant difference from the image below.

Could there be an error in the drawing that we have all been looking at and accepting as correct for all these years?

Your thoughts please.

Thanks in advance!

Sometimes illustrations aren't as perfect/accurate as we'd like them to be.

Just as rifle and pistol projectiles produce temporary cavitation as they traverse colloidal media, so too, do shotgun pellets, albeit at somewhat higher (required) velocites than their handgun counterparts.

According to Duncan MacPherson's penetration model, the calculated threshold velocity (Vc, in fps) for the production of temporary cavitation is dependent upon, and varies inversely against, the diameter of the specific projectile and its structural configuration. (FMJRN, FMJTC, SWC, WC, etc.)

Where a 9mm FMJRN produces temporary cavitation at velocities in excess of 515 fps and a .45 FMJRN does so at velocities in excess of 480 fps; shotgun pellets (ie: "buck shot") do so only at much higher velocities strictly due to their smaller cross-sectional area.

Here are the respective Vc values* for the commonly encountered ("anti-personnel appropriate") buckshot sizes:

OOO Buck (0.36") = 625 fps
OO Buck (0.33") = 642 fps
O Buck (0.32") = 648 fps
#1 Buck (0.30") = 661 fps
#2 Buck (0.27") = 682 fps
#3 Buck (0.25") = 698 fps
#4 Buck (0.24") = 706 fps

*Vc has been rounded to the nearest significant digit.

Above their respective Vc these configurations produce temporary cavitation, once they fall below their respective Vc they do not.

Hope this helps.

[Grytpype]

A sphere will make a temporary cavity. You can find an example of a sphere's wound profile in his article What's Wrong with the Wound Ballistics Literature, and Why, in his Institute Report 239 (and I'm blanking on the medical journal that published it as well). It's a lousy scan, but I found this wound profile in the article on-line.

[DocGKR]

Yup, spheres can make a small temporary cavity. But look what it took--an impact velocity in excess of 3300 fps to create a TC that is smaller than most rifle hits. Large caliber, heavy, relatively low velocity spheres can also create fairly large TC's (think .50-.70 musket balls), much like modern shotgun slugs. However, buckshot tends to offer primarily massive localized crush damage with minimal TC effects.

[Augusto]

Dr. Fackler´s profiles shows a small TC here
http://www.firearmstactical.com/imag...20Buckshot.jpg

and a big one here
http://www.firearmstactical.com/imag...ter%20Slug.jpg

[Blastem]

Thanks for your the thoughts, it spurred more thinking and more research.

I found several images with large temporary cavities, here are a couple of the better ones with an easy to read ruler.

Source: http://www.shotgunworld.com/bbs/view...109958&start=0

#00 Buckshot (Remington Express)
Composite photograph illustrating total penetration of one round of Remington Express 00 unplated buckshot.




The first block (right side) illustrating the temporary stretch cavity and the dispersion of the shot within the target media.


My measurement shows the temporary cavity was 6 to 7 inches depending on where it was measured.
-------------------------------
2¾ Federal 00 Buck Magnum (12 pellet) shot out of an 18 inch barreled Remington 870 marine magnum

"...Details of the large temporary stretch cavity and the entrance aspect. The temporary stretch cavity measured approximately 11 inches in length..."



Similar results were found by the folks at Brass Fetcher Ballistic Testing.

It seems to me that most would tend to expect that the shot gun would do more damage than a 30-30 round. The first image does not show the temporary cavity as it does for the other rounds and could lead some people underestimate buckshot performance. The photos from several sources seem to be a better representation.

The first image is fairly close to some photos of BIRDshot in gelatin and perhaps the original artist simply got them confused and mis-labled them after drawing?

Thanks again for your thoughts.

[Zhukov]

You'll notice that the gelatin blocks used in that shotgunworld article were grossly out of calibration. It makes the whole thing suspect.