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Old November 4, 2008, 02:15 PM   #1
300magman
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Bullet Diameter Vs Knockdown power

Ok, just an academic debate here. But what effect does bullet diameter have on knockdown power, all other factors being equal.

Lets say a 7mm bullet of 165gr moving 2400fps and a .30 (or 7.62mm) bullet of 165gr moving at 2400fps.

Now equal weight and equal velocity = the same energy delivered on target IF the bullet comes to a stop within the target.
But will the larger diameter bullet transfer the energy faster resulting in a significantly more "shocking" impact?
And if the bullets both exit out the other side of the deer, will the larger diameter bullet transfer significantly more energy to the target on its way through.

I guess my mind is made up that the 7.62 or 30 cal round WILL "hit harder" the question is, (if I'm right, lol) will the difference be significant or immeseasureably small.
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Old November 4, 2008, 02:20 PM   #2
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Larger wound channel.
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Old November 4, 2008, 02:48 PM   #3
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I think the larger surface area will create a more wound trauma.

Between a 7mm and a 7.62mm I'd be surprised if there is much difference. If they are both the same nose, like a FMJ, they would both enter at a point, just the other will split flesh .62mm wider, if you can tell through flesh.

With the little extra surface area the 7.62 will have more friction that would drag on it more, so the 7mm might travel through a little more material, but only a little.

It more matters on bullet design, unless you are comparing a .30cal to a .45cal.

As far as knock down power, I imagine if a needle shot through your body you could still run, but if a broom stick went though you, I think you would want to lie down for a while.
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Old November 4, 2008, 03:11 PM   #4
j.chappell
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Well here you go:

165gr Sierra GameKing BTSP 30cal bullet starting out at 2400fps will be traveling 2203fps and have 1778fpe at 100 yards and at 500 yards will be 1516fps and 842fpe.

165gr Sierra GameKing BTSP 7mm bullet starting out at 2400fps will be traveling 2226fps and have 1815fpe at 100 yards and at 500 yards will be 1606fps and 945fpe.

So, the 7mm bullet has a higher sectional density will have more retained velocity and energy at any yardage and therefore will have more killing power. Will it deliver more shock, given the fact that they are as close to the same bullet as far as design and make up as you can get, I believe so.

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Old November 4, 2008, 03:16 PM   #5
Brian Pfleuger
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The theoretical difference, in Thornily Knockdown Power, is 84 for 7mm and 88 for 7.62mm.

Theoretically, 4.761% more.
In reality, no difference.
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Last edited by Brian Pfleuger; November 4, 2008 at 04:14 PM. Reason: Highlight Intentions
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Old November 4, 2008, 03:34 PM   #6
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May be of some interest

http://www.eabco.com/swiftbulletco02.htm
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Old November 4, 2008, 03:47 PM   #7
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If by "all other things equal" I reckon you mean same POI? If so a direct hit on a vital organ is goin' to have similar results... But,IMHO and only IMHO, If you were off by a given distance with the larger diameter projectile and the dynamic shock wave ruptures a major artery/vein a slightly smaller one may not have enuff dynamic shock wave to do the same...
I guess what I am trying to describe is similar to comparing a M-80 chinese fire cracker tossed in a lake tied to a spark plug compared to a quarter stick of dynamite... I assure you more fish float up from the dynamite from a wider area than from the firecracker.
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Old November 4, 2008, 03:57 PM   #8
Brian Pfleuger
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All else being equal I'll take the larger bullet. If things like recoil in particular are not equal, I'll take less recoil. Might take more recoil for substantially better ballistics, if the range is expected to need it.... etc, etc


Good calculators for these sorts of questions here:

http://www.beartoothbullets.com/resc...m?bw=&bv=&cal=
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Old November 4, 2008, 04:03 PM   #9
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Quote:
what effect does bullet diameter have on knockdown power, all other factors being equal.
Knockdown power does not exist. It has been theorized by many gun writers and ballisticians, but no one has ever demonstrated that a bullet of larger diameter can "knock down" an animal. Possibly the fault of that pesky Newton guy and his laws. On the contrary, a smaller diameter bullet effectively transfers energy AND has better ballistic coefficient for a given weight. They seem to hit very hard also, possibly because to get a smaller diameter bullet to fly true you have to use a tighter twist, thereby increasing bullet upset upon impact. Roy Weatherby built a whole rifle empire on that basis.

Theoretically, larger diameter should provide a greater area of impact, but in reality there is little difference in effective frontal area with calibers typically used for game hunting on the North American continent. However, if you want to get extreme, a 4-bore rifle (1" bore diameter) will definitely let your game know you are serious.

Larger diameter bullets are usually heavier than smaller caliber projectiles. One thing that heavier bullets do well is penetrate through hard, tough, dense tissues like bone or heavy muscle, but few of us will ever need to test that because we primarily shoot thin-skinned, lightly muscled game on this continent, with the possible exception of large bears.
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Old November 4, 2008, 04:07 PM   #10
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Scorch, The boar hog has a much thicker skin protecting the vital zone than any animal I have seen with nearly 2 inches. I have seen well over 1.25 inch...
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Old November 4, 2008, 04:09 PM   #11
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Most who have posted here have missed the point you ended your post with: would it make a noticeable difference?

The answer being: Being gun enthusiasts, most would want there to be a significant difference. Some want it so bad that they will compare the two bullets at the far end of the range (500 yards), which is less likely to be the condition rather then more likely(almost all the deer I have shot in my lifetime were closer to the muzzle than to 500 yards...sometimes by design, sometimes by circumstance).

In reality, there is not likely to be a measurable statistical significance difference between the two calibers (about 4% the guy says?). However, we are all human and we need fodder for discussion on our favorite subject, and excuses to obtain new and exciting guns, calibers, et. al. It is not likely the deer, elk, etc. would notice any difference at all...the proverbial ingenious solution to a non-existent problem.
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Old November 4, 2008, 04:21 PM   #12
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diameter of bullet being:

Quote:
...Between a 7mm and a 7.62mm I'd be surprised if there is much difference. If they are both the same nose, like a FMJ, they would both enter at a point, just the other will split flesh .62mm wider, if you can tell through flesh...
Whoops! 7mm = .284 inch. 7.62 =.308 inch. The difference is .024 inch. A sheet of paper is about .004 thick. .024/.004 = 6 thicknesses of paper. Wrap a piece of copy paper around a 7mm bullet three revolutions and see if it produces a "big" difference in diameter.
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Old November 4, 2008, 05:03 PM   #13
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Diameter in and of itself isn't likely to be a huge factor, but increased diameter usually gives the option for increased weight which can be significant.
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Old November 4, 2008, 08:57 PM   #14
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Quite a discussion...I did like that article about medium velocity bullets though. Kinda reminds me about the topic that eventually led me to write this post.
A friend of mine told me that while a 300RUM was a great 300 yard deer rifle his 30.06 would kill deer twice as dead at 50 yards. His reasoning being that a 150 gr bullet fired from each would be going so fast comming out of the RUM that it would "laser through" a deer at 50 yards and make a pin hole so quick and smooth that no shock would transfer to the deer and the wound channel would be tiny compared to the slower 30.06 which would impart significant "shock" into the deer.
I don't know about his "laser" theory but I don't argue with him on the last point, I've seen what my and his 30.06's can do at 50 yards and the damage to even a well struck deer does indicate some real "shock" to the area surrounding the entrance and especially exit wounds.
This kinda lead me to think, would 30 cals "laser" less than 7mm and from there this post was born.

But as said...what deer would ever know the difference ?

On a different note, when people say "knock down power" I don't think of it like being hit with a bag of cement has more knock down force to it than being shot with a .22 To me its not about physically shoving the target, I take the term to mean how quickly a animal is killed or how fast a bullet throws the switch from alive to dead....instantly or over 2 seconds or over 10 etc. Thats what I personally call knock down power. As stated, Newton's laws (equal and opposite reactions) perclude a bullet actually picking a deer up and throwing it over...unless the shooter landed on his ass too.
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Old November 4, 2008, 10:40 PM   #15
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Quote:
A friend of mine told me that while a 300RUM was a great 300 yard deer rifle his 30.06 would kill deer twice as dead at 50 yards. His reasoning being that a 150 gr bullet fired from each would be going so fast comming out of the RUM that it would "laser through" a deer at 50 yards and make a pin hole so quick and smooth that no shock would transfer to the deer and the wound channel would be tiny compared to the slower 30.06 which would impart significant "shock" into the deer.
Tell your friend that he is completely wrong. If anything at all the bullet from the RUM would come apart at near muzzle velocity. There is an inherent need to use premium bullets in magnum calibers where a close shot may be taken. Anything less will come apart dramatically.

Why would you even use the 300RUM when you may be taking 50 yard shots? Now I realize that in hunting you may get a shot at any distance but if your hunting includes those 50 yard shots then I believe you are carrying the wrong weapon if equipped with a rifle chambered for the 300RUM.

Sorry I just can’t believe all the people that bought that rifle as the "ultimate deer rifle". That’s like using a 22-250 for rabbits that you intend to eat, lol.


J.
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Old November 5, 2008, 12:17 AM   #16
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Quote:
Scorch, The boar hog has a much thicker skin protecting the vital zone than any animal I have seen with nearly 2 inches. I have seen well over 1.25 inch...
Yes, Brent, I know, and I killed dozens of big hogs with my 30-30, 7X57, and 243. Biggest was around 350 lbs, most 200-250 lbs. Even used a 45 ACP on a few. I prefer the sows for meat, but the boars look meaner when you show them off to the locals.
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Old November 5, 2008, 12:22 AM   #17
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"all other factors being equal."

The problem is all other things are not equal.
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Old November 5, 2008, 12:46 AM   #18
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Funny that no one has mentioned meat retention, my first thought.

When the Mini-14 first came out we all thought that it was going to be the ultimate swamp rifle. Our deer tend to be small and the Mini proved to remove way too much meat from the exit side. Too much velocity.

If I've learned anything over the years it's to expend the energy in the animal. A pass through means that you lost something, maybe a lot.
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Old November 5, 2008, 09:44 AM   #19
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True enough J. a 300RUM is indeed overkill even on large deer at most moderate ranges....it was just a statement for debate, or an opinion. I don't actually own a RUM yet, and I'm still debating if I ever will. But if I do, I won't be firing it 50 yards with full power loads.

If I did carry one at closer ranges I would surely use that power level one ammo from remington where the rounds have 30.06 equivalent velocities. (Or similarly loaded down handloads)
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Old November 5, 2008, 09:51 AM   #20
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Quote:
it was just a statement for debate, or an opinion.
All due respect, but what your buddy was telling* you is not open for debate or even an opinion. He's flat out wrong. Please don't take this as a personal attack.

Quote:
*His reasoning being that a 150 gr bullet fired from each would be going so fast comming out of the RUM that it would "laser through" a deer at 50 yards and make a pin hole so quick and smooth that no shock would transfer to the deer and the wound channel would be tiny compared to the slower 30.06 which would impart significant "shock" into the deer.
I'm not sure what overkill is, but I see no need to put up that level of recoil to shoot deer. More than enough gun shouldn't bring a hunter a higher level of confidence. That hubris can blow many a shot.
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Old November 5, 2008, 09:57 AM   #21
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300magman,

Exactly, I do not see why some feel the need to buy all of these magnums, buy super premium ammunition and shoot there deer at 35-100 yards. If a guy says because I want to, that is more than enough reason for me, but don’t tell me it’s because it is the greatest deer rifle to come along in recent history, just tell everyone it is because you wanted one, that my friend is justification enough for just about anything.

I do own and use magnums but I use a handload appropriate for the situation. I have used my 257 Weatherby a lot for hunting locally. I have a farm I hunt on that I may get a 25 yard shot or I may be faced with a 300+ yard shot, so I use a partition. They stand up to up close shots, do not tear apart an animal, but yet perform at the greater distances that I often encounter.

J.
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Old November 5, 2008, 10:44 AM   #22
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1st off, from the examples you used, IMO, not enough of a difference...

I've posted similarly before, but as the "new guy" to my father in laws hunting party ( many many years ago )... I got to do most of the field dressing of the deer ( I guess they wanting to make sure I knew how )... early on, I used a .243, nearly everyone else used a 30-06, the owner of the hunting land shot 300 Win Mag, & in the later years, I used a 45-70 Marlin...

as mentioned earlier, it's pretty hard to make everything equal... but the 45-70 made smaller bruised ( blood shot / wasted meat ) areas than the '06's, the 300, or the .243... however, that is due to velocity...

my personal opinion, if you could make everything equal ( impossible, without increasing the velocity of the smaller bullet, without decreasing the larger bullet's velocity to an ineffectual level ) the 45 should have more knock down than the 22...

but because you have to increase the velocity of the smaller round, the hydrolic shock is an impressive force on tissue... probably even more so that the force of a big fat meplat spanking the side of an animal, at a much decreased speed...

... however, in my exprience, the 45-70 plants deer slightly better than the 243... if engine room trama doesn't result in instant death / interupted nerve communication between the brain & the body
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Old November 5, 2008, 01:36 PM   #23
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I've read everyone's posts, and I agree with those that say it won't make a SUBSTANTIAL difference in the real world of hunting. Yes, using the ballistic coefficients of the two bullets there will be a slight difference in the two, but just not enough to make a practical difference. That's my nickel's worth to an interesting thread.
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Old November 5, 2008, 11:39 PM   #24
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ummm, don't the bullets expand???

.005 difference in brass thickness of the bullet, and different shape of the nose makes a MUCH bigger difference then a bunch of difference in diameter of the bullet coming out of the rifle.

for simplicity, damage to the animal is a function of the energy the bullet has when it hits the deer, minus the energy the bullet has after it goes through the deer.

If we assume the bullet doesn't go through the deer, then the question becomes where in the deer does the bullet expend its energy.

A bullet that fragments on impact will blow a large entry wound, and not even make it through an elk's shoulder.

A bullet that holds together too well and doesn't expand will drill through a deer without expending all of its energy.

Is this a function of time? Sort of. Is it a function of what the bullet hits? sort of. Is it a function of bullet jacket design? ABSOLUTELY.

Is it a function of bullet caliber, if you took out the bullet design from the equation? Absolutely not, unless you are comparing two bullets of different calibers neither of which mushroomed.
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