Does muzzle energy = "knock down power"?


September 8, 2007, 08:41 PM
I'm recontemplating my handgun choice because of several reasons and I noticed that the .40 S&W has more muzzle energy than the .45. Ex. Blazzer .40 180 gr @ 1,175 fps = 475 ft-lbs where as .45 230 gr @ 845 fps = 363 ft-lbs, a difference of over 100 ft-lbs. I was just wondering, not worrying about wound channel size or any of that stuff, does more muzzle energy mean more "knock down power" to be transferred to the target?

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September 8, 2007, 08:59 PM
not completely, it means that more energy is availible to be tranfered to the target. if the bullet passes completely though the target some of the energy was not tranfered to the target. for maximum energy to be transfered to the target the bullet should stop just under the skin on the off side or drop to the ground immediatly after leaving the target.

September 8, 2007, 09:01 PM
Do you really think it matters? Both 40S&W and 45 ACP are good cartridges.

September 8, 2007, 09:01 PM
yeah, such as the reason to use a good hp, to provide more surface area to transfer energy.

But another question. would a gun with more muzzle energy be better for shooting tough and thick skinned animals (not like elephants or elk or anything like that) or light armor such as car doors or walls.

September 8, 2007, 09:11 PM
A lot more than energy is involved in penetrating tough barriers. The 223 Remington has a lot of energy, but penetrates poorly for example. Bullet construction, sectional density, etc, play an important role.

September 8, 2007, 09:26 PM
Does muzzle energy = "knock down power"?

Short answer: No.

For historical perspective see Hatcher's Formula as discussed in Hatcher's Notebook and Taylor's Knock Out as in Taylor's book or as googled or found on Wikipedia. For a modern perspective google a little bit - Fackler and Sarnow and Evan P. Marshall and lots of names will get you started.

Finally of course knockdown power as commonly used is a misnomer although a .577 or .600 or .700 does seem to be properly called a crumpler in some circumstances. Then too a hit in the head with a thrown baseball has lot of knockdown power on people even a medicine ball to center of mass.

September 8, 2007, 09:27 PM
when you factor in penatrating barriers then bullet weight and construction become equally important as availible energy.:D

September 8, 2007, 09:38 PM
Proper bullet placement and adaquate penetration equals knockdown power. Look at the Reagan assisination attempt, two well placed .22 rounds on unintended targets were true one shot drops taking them out of any fight, a poorly placed round on the intended target and he didn't know he was shot until he saw the blood.


September 8, 2007, 10:20 PM
at what distance does the .45 have more kinetic energy than the .40

September 8, 2007, 10:23 PM
knockdown power assumes a constant as a target. at what distance are you comfortable with being shot with a .40 rather than a .45? :D

September 8, 2007, 10:29 PM
Energy is only a major factor above approximately 800 ft-lbs. At energy levels below that, the direct crush mechanism reigns supreme, which will primarily be based on expanded diameter and penetration depth.

Jim K
September 8, 2007, 10:31 PM
There is really no such thing as "knockdown" power. Tests on various dummies, as well as on people wearing bulletproof clothing pretty well show that no gun that can be held in the hands will knock a person down. A person who is shot falls down because he is seriously wounded or dead, not because some super-duper bullet knocked him down. Only in the movies, and with the help of a special harness, do people hit with an ordinary bullet go flying ten feet through the air.

A case in point - When the good Bishop-turned Confederate General Leonidas K. Polk, was sniped off Pine Mountain, Georgia, the projectile reportedly passed completely through his body but left him still standing. The weapon was a 20 pdr Parrott rifle, which was without a doubt, the largest sniper rifle used in any war. (I think it is legitimate to call it a sniper shot because it was deliberately aimed at a small group from a long distance, almost a mile.)


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