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Killing Power : Formulas/discussion

Old 11-20-2013, 01:30 PM
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Post Killing Power : Formulas/discussion

The Hornady site gives a big 200yd power advantage to the .17Hornet 20gr over its' .22Hornet 35gr ammo. What the heck?
http://www.hornady.com/store/17_horn...mance-Varmint/
Would the lighter .17H be a more reliable kill past 100yds than its' 22 brothren; both share the same casing? 20gr is pretty lite.
http://www.hornady.com/store/22-Hornet-35-gr-V-MAX/
What other factors, ratings, and such indicate the animal (?yote) will drop or only run a short distance?

Last edited by Sosalty; 11-27-2013 at 12:39 PM. Reason: lighter not kighter
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Old 11-26-2013, 10:25 AM
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You gotta look at the formula behind the numbers.

Ft/lbs is a reference to kinetic energy.

Kinetic energy is found by taking the bullet mass (m) and multiplying by the velocity squared (v^2) and finally dividing that answer by the constant 450,240.

mv^2
450,240

There are a couple other formula that will all arrive at basically the same answer... but since this is the one I learned for archery, that's what we will go with.

The other one you can use is 1/2 of the mass times the velocity squared... more of a classic high school physics formula 1/2mv^2.

In either one of these forumlas... you can see that kinetic energy relies much more heavily on VELOCITY than it does on mass (bullet weight). So any bullet going faster is going to have a higher kinetic energy than a heavier bullet.

What a light bullet doesn't have.. is momentum. Would you rather be hit by a tennis ball going 150 mph or a baseball going 100 mph? Anybody with any sense will take the bruise and the tennis ball over the broken bone and the baseball.

Additionally, you need to look at the power to target weight ratio. A 5# ground hog being hit by a .17 hornet bullet @ 100 yards with an energy of 421 ft/#s.... that is a 1:84.5 ratio of target mass to bullet energy. You can basically think of it as resistance. No doubt that bullet impact would blow that groundhog off its feet... it is about the equivalent of a full grown man being hit by a sub-compact car.

Now, "energy" isn't what kills an animal hit by a bullet. There is no magic shockwave or electrical discharge that occurs... bullets kill (with very little exception) the same way that arrows or knives do... they allow blood loss which diminishes oxygen to the brain... lights out.

Now, lets take another example.. lets use a 750# elk and the same .17 Hornet at 100 yards... now that ratio is 1.78:1 in favor of the elk. The elk ain't gonna move.

As it pertains to "killing power", there are in my opinion, three things that will make a cartridge more adept at taking game than another:

1) Bullet placement.... you miss... you lose. So a cartridge that is accurate has an advanatage over one that is less so... this correlates directly with shooter comfort also. A 12ga slug has more "killing power" than a 22 LR.... yet, 98% of the people in this world will shoot more accurately with a .22 than a 12ga slug, and only a small percentage of slug guns are accurate enough to kill a squirrel everytime at 50 yards, and even then only in the right hands. Any .22 should be able to do this... and this is a very basic marksmanship goal... so here, the .22 would actually have more 'killing power' or should I write "potential" than a slug gun.

2) Bullet construction. A bullet that isn't tough enough to get through whatever it needs to get through and make it to the vitals is WORTHLESS.

3) Momentum. The bullet needs to be heavy enough with enough velocity not to veer off course when impacting bones and the like and continue onto the vitals. Momentum is found by multiplying mass by velocity... both things are weighed equally.


As far as the killing power of ballistics.... I am sure you can kill game with ballistics tables... but frankly I can't throw them hard enough.
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Old 11-26-2013, 03:20 PM
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1.) You guys are over thinking this.

2.) You have two much time on your hands.
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Old 11-26-2013, 08:37 PM
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Thanks SwampCollie,
I just have to know so much before I commit to investing in a set up, possibly the 22 Hornet. Folks often throw contradictory claims around when a generic realistic report, to serve as a starting reference point, would be easy from veteran shooters.

My experience has been to invest in a pcp air rifle or a pistol, complete with tools, airtanks, reloading dies, so forth. . . then wish sought after advise would have been more available. Fired my 30-30 the other day and it took 3-4 secs for the rifle retort to fade out (sounds kinda cool booming down the creek). My situation is here's 6 houses within 300yds of my place: most the wildlife travels below me along the creek so shooting can take place safely downward into the far bank.

Daybreak is the choice time to remove 'yotes. I'm thinking along my 22WMR with a suppressor. Shots are inside 60yd, prefer to keep peace with neighbors, and don't want the wife to ban shooting from our porch. The area is covered up in Bobcats and 'yotes. One bob and 2 yotes have been removed this fall. I still know of 4 other bobs and yote howling is coming from every hill. More than 'occassional' shooting is called for.

Interesting to know that formulas often give more weight to velocity. Simple to X's weight and velocity and bet it's more representative of killing potential. Plan to weigh yotes in the future and continue to asses bullet/wound characteristics.

Last edited by Sosalty; 11-26-2013 at 08:51 PM.
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Old 11-26-2013, 09:43 PM
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The divisor should be 450,380, not sure who used 32.16 first, I've seen it published in a few different places that way, but gravity is 32.17, not 6.

For those not following: ke = 1/2 m v^2, with correction of units: 1/2 m/7000/32.17 v^2. 2 x 7000 x 32.17 = 450,380.

Swamp collie is giving the same formula twice, just not realizing that the 1/2 mv^2 and mv^2/450380 is the same formula, just with the unit conversion from grain ft^2/s^2 to ft.lbf. is completed already for the second version.

Last edited by Nomercy448; 11-26-2013 at 09:47 PM.
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Old 11-26-2013, 09:57 PM
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Originally Posted by Sosalty View Post

Interesting to know that formulas often give more weight to velocity. Simple to X's weight and velocity and bet it's more representative of killing potential. Plan to weigh yotes in the future and continue to asses bullet/wound characteristics.
Kinetic energy varies exponentially with velocity. Ammo manufacturers like ke because foot pounds force seems like a measure of killing power.

As you noted, MOMENTUM, simply MV, is what really matters. Newton's law restrains that momentum is conserved, not energy, so it is a better measure of penetrating and killing power.

I generally use MV/7000, which converts grains to pounds, giving units of ft.lbm./s, a common momentum unit. These numbers will be single to double digit, rather than several thousand if you don't convert to pounds.

Another momentum killing factor is the Taylor KO factor. Simply momentum times bullet diameter. This is a gauge to compare stopping power of similar momentum bullets, with different diameters. MVD/7000=TKO The TKO factor helps explain why moderate loads out of a .45-70 seem to hammer deer even though a .30-06 has more energy.
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Old 11-27-2013, 09:30 AM
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Originally Posted by OhioNovice View Post
1.) You guys are over thinking this.

2.) You have two much time on your hands.
Sittin at work getting paid to wait until something happens.
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Old 11-27-2013, 10:29 AM
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Well placed shot = killing power

Simple !
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Old 11-27-2013, 11:05 AM
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Default Useful killing power formulas

OhioNovice
"1.) You guys are over thinking this.
2.) You have two much time on your hands."
Just retired, house hubby, life is good when she gets home and catches me mopping without a shirt

1 generic Ft/lb ratings,
2 Taylor Knock Out Factor,
http://www.reloadammo.com/tkofactor2.htm
3 OptimalGameWeight (see post below)
4 HITS http://www.hornady.com/hits/calculator(This one is basically bullet weight X velocity as mentioned)

Somewhere I came across a formula for optimal game weight matched to the cartridge. Informative, I remember the optimum weight of game for a .223 at 200yds was 20lb.

Sheridan, yeah, blowing your aim preempts any power or positive considerations, except to learn to not take some shots.

Last edited by Sosalty; 12-06-2013 at 07:53 PM. Reason: option gawck hairball optimal
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Old 11-27-2013, 05:53 PM
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Originally Posted by Sosalty View Post
Somewhere I came across a formula for optimal game weight matched to the cartridge. Informative, I remember the optimum weight of game for a .223 at 200yds was 20lb.
Usually you'll see OGW tables (optimum game weight) more often than as a formula. Tabulation gives a better opportunity to set barriers between types of game, i.e. it takes proportionately more or less ft.lbs. per pound of game weight to kill certain classes of animals than others (pattern doesn't always follow the way you might expect though!!!).

It's not that difficult, math or not. Hunters that came before have proven what works well, what "just kinda works", and what really doesn't work.

Too much time on my hands? Maybe so. I'm very blessed in my career to have the freedoms that I have.

Last edited by Nomercy448; 11-27-2013 at 05:55 PM.
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