Momentum or Energy?

[flyboyjake]

This may be the wrong place for this topic, but here goes anyway...

You are planning on rolling up a load for your 10mm (because its your favorite caliber ever) for a back country hike in the Montana wilderness. Its intended purpose is to defend you from any dangerous wildlife you may encounter. Your two choices for this topic are as follows.

Weight Velocity Energy Momentum
135gr 1600 767 30
200gr 1300 750 35


I have struggled with the concept for some time, and the industry seems somewhat torn on it too...While I understand some of the concepts behind the principles of conservation of energy and momentum, and the elastic/inelastic collision differences, I dont fully understand the difference between momentum and energy...they use the exact same variables to derive from, except energy is highly velocity dependent... It would seem to me, than in the woods, and even in many human interactions, one would want their bullet to be able to penetrate...This to me would depend on a bullets momentum, and its frontal surface area on impact...

The simple question is what load do you choose, and why?

[Brian Pfleuger]

The only wildlife that really qualifies as dangerous under normal circumstances (that would need a gun) would be bear. Where bear is concerned, you need penetration. Penetration comes from momentum, not kinetic energy. So, momentum is what I'd load for. Most other times, I go for light and fast.

[Ike666]

FWIW, I was reading Hatcher's Notebook this weekend and he said that 60 ft-lbs of force was the minimum needed to do grievous bodily damage to a human. This is in the section on shooting straight up to see how far and how fast on return. Interesting.


Don't know about them bars out there, but either one will lay waste to a hummin' bean.

[glockcompact]

I too load for 10mm because, well because its so awesome. Like written above from what I understand you will be better served by using momentum. Them 200 grainers will be quite nice. That's what I load for back country in Co.

[Tex S]

I would choose the 200gr load.

Maybe a 180gr Speer GDHP?

[snuffy]

There's a lot more to this than energy and/or momentum. There's bullet construction, combined with what body type the target has . A bear, more specifically a grizz, is a very heavy boned dense, muscular animal with a bad attitude. Hurt it, it just gets a worse attitude. Most guides will tell you to aim for the shoulder, to "break it down". That means to break the front shoulder or leg bones, then shoot for the heart.

Fragile bullets like the gold dot would be worthless, it would hurt like he!!, get him real mad.

Another problem is accuracy when a charging grizz is getting closer. A semi auto is great in that scenario, but how many good hits will you make while yelling at others in camp or on the trail to run while you face the bear? I duunno how many rounds a 10 holds, but filling the air with bullets won't do much good.

If I had to choose, I would go with a 200 in a full metal jacket. It might break a shoulder, and might get to the heart.

[Tex S]

Fragile bullets like the gold dot would be worthless,

I haven't personally tested any Gold Dots, but don't they have a reputation for being a pretty tough bullet? Not like an fmj, I know, but still pretty tough.

[flyboyjake]

Ill agree with the fact the bullet construction etc... has much to offer as well, however for the sake of the topic, lets assume they are both equally constructed.

Manufacturers tend to flaunt muzzle energy more and more as the bullet weight is reduced, implying a lighter bullet at high speed is the end all be all of your caliber choice...The purpose of my question was to try to gain some perspective on how everyone else sees the momentum vs energy debate.

[Brian Pfleuger]

Manufacturers advertise what sells, nothing more.

Look at the archery world.... all you see is speed, speed, speed... and every bow made is more than fast enough...most shots are at 15 yards and the deer wouldn't know if that arrow was going 210fps or 350... most shops you can hardly find a back tension release, yet virtually 100% of serious accuracy shooters use them....

Firearms and ammunition are the same story. SPEED!! ENERGY!!

Now, if you're shooting prairie dogs at 400 yards, all you need is SPEED (energy) and ACCURACY, momentum is fairly well irrelevant in terminal performance.... but if you're shooting a water buffalo at 45 yards, you may get ONE chance and you may be dead if you screw it up. They are big, strong, thick and solid. You need penetration. MOMENTUM equals penetration. Kinetic energy just comes along for the ride.

[flyboyjake]

peetza, I believe I share your sentiment. These gimmicks like the taylor knock out factor and such, seem to set the enthusiast or amateur back a few steps in terms of shooter education. For a long time it has worked on me...and its taken much effort to sift through all the BS to find info I can put my faith in.

[jmortimer]

You want momentum. The 10mm is close to .357 and even in .357 you want an 180 grain bullet in the woods and the 180 to 200 gain in the 10 mm. Think of this, a .45 Colt even at standard pressure, shooting a 255 grain SWC at 950 fps will shoot through most any animal on a broadiside even at 450 ft lbs whereas a
.223 at about three times the energy is "less gun" in the woods.

[SL1]

then you need to think about penetration. And, momentum is just part of the penetration recipe. You also need a bullet that is constructed to that it will penetrate instead of flattening, shattering or deflecting. And, once penetration is achieved, there has to be enough remaining energy to damage the vital area.

In big bears, that is a lot to ask of a handgun bullet. Heart and lungs are pretty deep and pretty big, and the bears are tough enough that they can keep on coming for way too many seconds after they get hit there.

If you really need to drop a bear that has reached you, you need a bullet that will get into its skull. Even a heavy bullet may not do that if it has a soft nose. There is a write-up about a park ranger that shot a grizzly 5 times in the head with his service-issue .357 Magnum JHPs, without stopping the bear (which had ahold of his legs). His last shot was up under the bear's chin and into the spine behind the head, which dropped the bear. After the incident, autopsy of the bear showed that the JHPs had pentrated the surface skin and muscle but flattened against the skull bone and slid along the surface of the skull under the flesh. The soft noses deformed and essentially provided a ramp to deflect the momentum.

From this, I concluded that a "bear defense round" for a handgun should have a wide, HARD nose with an edge that will "bite" into the bone and tend to keep going straight. A hard cast lead bullet will do that better than a JHP or JSP. But, the best is probably the turned-brass "Grizzly Punch" bullets that have wide meplats, sharp edges and are much harder than lead. At one time, I think they made those in .357" diameter, but now they list nothing less than 0.430" diameter. So, those of us who carry something less than .44 Magnums need to think about hard lead.

From what I have read, heat-treated lead in the 30 BHN range does not shatter, while pure Linotype alloy (about 24 BHN) does shatter. So, I tend to favor heat-treated bullets in the 20-30 BHN range, with something like the LBT "wide flat nose" design.

But, I have never SHOT a bear with any of those choices, so this is just arm-chair engineering on my part, so far.

SL1

[Slamfire]

Momentum is conserved. Mass times velocity. It is one of those laws of physics, conservation of momentum. Momentum is conserved in collusions, not kinetic energy. Kinetic energy is Momentum time velocity. It is very easy to boast velocity by 10 fps and increase KE by 100. It is a lot harder to increase momentum by 100.

Momentum kills. People get killed all the time by large things going slowly. I will bet that dropping a 50 lb sack of cement from a roof top on someone will kill them. Not much velocity, but lots of momentum.

Bet that an increase of that 5 foot pounds of force hits a lot harder on both ends than it looks.

What handgun puts out 35 foot pounds of force? I thought a 30-06 puts out 14 ft pounds.

[flyboyjake]

the units are a bit different than you may be used to seeing. I am using units that are used by the shooting world as opposed to physicists. Those momentum figures were in "grain FPS". The 30-06 comes out at about 66.

Momentum is conserved in both elastic and inelastic collisions, while energy is conserved in only inelastic...I think thats right...

So for smaller game or personal protection, do you all use high energy projectiles? I still think a high momentum gold dot will do more damage than a low momentum but high energy gold dot... I believe that high energy bullets expend a very high amount of that energy trying to expand the bullet on impact. I d like to see a study to determine how much energy goes to what task.

[SL1]

Think about it.

When you shoot a gun, you absorb MORE momentum than the game animal.

Besides the fact that you need to absorb the momentum associated with the MUZZLE velocity while your target sees only the remaining down-range velocity of the same projectile, there is also the momentum that comes from the powder gases going out of the muzzle even faster than the bullet. (The recoil from the gases can be 50% or more added to the recoil from the bullet alone.)

So, shooting anything that weighs as much or more than you do would have to be lethal to the shooter in order to be lethal to the game IF it was just a matter of momentum that kills.

SL1

[flyboyjake]

I dont agree with that. You absorb an equal amount of momentum as a game animal would if he was at muzzle length. Bullet momentum is derived from the weight of the bullet multiplied by its velocity, so the gases and anything else are immaterial to how much momentum a bullet in travel has. I would agree to the notion that anything with enough momentum to knock over a game animal with as much mass as I do would also knock me over, but momentum isnt just used to knock things over. An object with higher momentum will be more difficult to stop. It will not knock anything over because the limitations of tissue and muscle will cause them to give way instead of maintaining rigidity.

Now when we talk about energy we get into extraneous variables. for example, a bullet has 300 ft lbs of energy, but it takes some of that energy to make the noise of impact, it takes some energy to heat up the target due to friction, it takes even more to deform the bullet after impact. How much energy actually goes into the target?

This kind of talk makes my head spin, so let me know if I made no sense.

[Brian Pfleuger]

I think we're splitting hairs a little, gentlemen.


Momentum itself doesn't kill.

Momentum produces penetration. The damage done by that penetration is what kills.

A person (or animal) can EASILY absorb the momentum of even a VERY powerful rifle round with little, even no, apparent damage, so long as penetration is prevented.


Damage to tissues/organs kills. Penetration causes that damage. Momentum causes penetration.

[chasep255]

Well if it helps each is computed differently.

Momentum
Momentum = Mass * Velocity or more simply as p = mv

Muzzle Energy
This is the kinetic energy of the bullet.
E = (1/2) * Mass * (Velocity Squared) or more simply put E = (MV^2)/2


It seems that velocity is more of a factor when it comes to Muzzle Energy and both the mass and velocity are equal with momentum.

[ipscchef]

I will do my best not to sound too much like an idiot with my thoughts, engineering formulas are something I cannot grasp, but should we not be talking first off about bullet construction over any Momentum vs. Energy theory? It would seem to me that the 200gr. bullet is the obvious choice here over a 135gr. I load for the .41 mag. which I believe is similar to the 10mm. You do not state the type of gun you are loading for, but if it is a revolver, then I would go with the Cast Performance 265gr hard cast bullet if it will fit. Like Peetza said, getting through all of the mass of a bear and into the vitals requires that a bullet stays together first and formost. A bullet of this type will give you the best chance of this.
I do not load for the 10mm yet, but would like to get both a semi and a revolver at some point, so I do not know what the heaviest cast bullet you can put into one, but I would find out what that is and develop a load using that bullet.
And I would respectfully disagree with Peetzakiller on one point, there are many other critters out there to be worried about. Having spent some time knocking about in the west, 'Yotes, ferel dogs, and two legged varmints present a problem more often than bears IMO. If bears are your main concern, as much as I like my .41 mag with 265gr. Hard Cast bullets, I would not feel overly confident with it against a big bruin. But it would do a fine job on just about anything else.
If this is an exorsize in theories, then I apologize, my answer is for a real world application.
JMHO and as always,YMMV
Willy

[alabama]

I would use a 200 grain xtp loaded to about 1250 fps. Hard cast penetrates better but i think ur more likely to get in a gun fight with a crazy mountain man then get mauled by a bear, i think with the xtp you would be prepared for anything. Good all around load.