help me understand bullet weight an kinetic energy

[gofastman]

Ok, I understand most handguns short of a super-hot 44mag wont give the elusive hydrostatic shock effect, so I'm gonna ask about slug penetration.
I'm looking at doubletaps hardcast loads and trying to decide between their 200g or 230g bullets, the 230g has significantly less muzzle energy than the 200g load yet allegedly penetrates more, if they were to be fired from a 6" barrel they would produce (according to my guess that a 6" barrel adds 75 fps) 840ft lbs for the 200g and 730 for the 230g.
at these levels, wouldn't the 230g penetrate almost too much, even for the large 4 leg critters, making the extra energy of the 200g round desirable?

 

[rmfnla]

Penetration is a function of two factors; bullet velocity and bullet momentum.

If you fire two of the same bullet at different velocities the one going faster will penetrate more (increased velocity).

If you fire two bullets of different weights at the same velocity the heavier one will penetrate more (increased momentum).

(If one bullet expands more than the other (as the faster one is likely to do) it will lose momentum due to its increased drag. The velocities you mention should not expand hardcast slugs, though, so that is not a factor here.)

You case has many variables, but by using the basic formula F=MV (Force = Mass x Velocity) we see that 200 grains @ 840 fps yields an unconverted factor of 168,000 and230 grains @ 730 yields 167,900 (virtually the same), so in this case the heavier bullet would probably give better penetration based on increased momentum.

 

[rcmodel]

Three factors actually.
The sectional density of the bullet also plays a very critical part in penetration.

That is weight for caliber, or the ratio of an object's mass to its cross-sectional area. The heavier it is for caliber, the higher the sectional density will be, and the better it will penetrate. (Like a spear)

But, that only applies to bullet that do not expand.
An expanding bullet of the same weight, velocity, and Sectional Density will not penetrate as deeply because when it expands, and sectional density is cut in half or more.

It's just like popping the drag chute out the back of a Funny Car dragster.

BTW: Energy figures are very nearly meaningless when it comes to bullet performance.

A heavy for caliber bullet (high SD) at low velocity would produce less energy, but penetrate much deeper then a lighter bullet (low SD) at higher velocity & higher energy.

rc

 

[481]

rcmodel's got it right.

Sectional density and impact velocity govern penetration in all media.

A much (over)simplified equation for the penetration of a bullet in calibrated 10% ordnance gelatine is:

[[Mass (grs.)/7,000] ÷ Diameter (in.)] x Velocity (f.p.s.)] ÷ 5.5 = Penetration (in.)

For example:

The penetration of a 9mm 124 gr. FMJ @ 1,120 fps in calibrated 10% ordnance gelatine would be calculated as...

P = [(124/7,000/0.355²) x (1,120)] ÷ 5.5

P = [(0.14056168) x (1,120)] ÷ 5.5

P = [157.4290815] ÷ 5.5

P = 28.6235 inches

 

[rmfnla]

Good info; thanks!

 

[MCgunner]

rcmodel's got it right.

Sectional density and impact velocity govern penetration in all media.

I'm in total agreement.

On the subject of "shock" or the effects of the ballistic pressure wave, i've seen much evidence of this killing animals with the .357 magnum. I agree, though, that smaller calibers, this is not a big factor. I shot a pig the other day, just shy of 15 yards, square in the forehead above the eyes. The bullet was a 140 grain JHP moving something shy of 1400 fps. At the shot, the pigs right eye blew out of it's socket. My thoughts are that the ballistic pressure wave inside the skull is what caused that. It was kinda cool if a little macabre. Of course, the pig died without a fight. That shot would have killed him with a .22LR, just sayin', the eyeball thing was evidence there is something besides crush cavity going on there with a hot .357 magnum load. I've shot a lot of pigs in the head in my trap, mostly with .38s. I never saw the eyeball blow out like that. Pretty wicked stuff. I've noticed tissue damage well away from the wound channel with the .357, too, using a 165 grain SWC at 1470 fps MV. Can't tell me the .357 ain't enough to cause some pressure wave effects as described by Dr. Courtney. Anything n the 400 ft lb range like I carry for self defense, I am more concerned with penetration, expansion in that it affects crush cavity. I do carry that 3" .357 occasionally, though. I pity the poor fool that has to be shot with it.