(With apologies to Tim Taylor and Tool Time)
The Power of the Rifle
(Some thoughts on what makes one cartridge "better" than another.)
Ah ha! Now we come to a controversial topic. It probably should really be under the heading of "Terminal Ballistics," but for now we'll discuss it separately. The topic is "power" and just what "power" increments are meaningful. As with the pistol, the way that a rifle bullet works is by creating as much permanent damage as is possible and what does this is the destruction of tissue by the bullet's passage.
The trick is to determine the damage level you need for your intended target and to then choose your weapon. It stands to reason the bigger and/or more dangerous your target the more damage you need/want to do. As a bonus, with rifles we don't have to worry much about a "power ceiling" as we do with pistols because controllability is not the big issue it is with handguns, so make the biggest and deepest hole you can with all the gun you can handle.
Unfortunately, there has never been the level of study put into the effectiveness of rifle ammunition that has gone into pistol ammunition so a lot of myths still exist for the rifle shooter. Let's see what we can discover together. You can email your comments and ideas to me by clicking here but if you violently disagree with my thoughts please don't waste your time trying to flame me as my delete key is within easy reach. Intelligent correspondence is welcome.
If one is to believe the ammunition manufacturers and the so-called gun rag "experts" all one needs to do is to drive a given bullet faster and faster to get more "power." If one looks at the kinetic energy figures one simply needs to drive one's bullet to the next increment up in KE and you are ready for bigger/more dangerous game. According to them, "out there where the game is big, instead of your puny little .308 what YOU need is the new.300 Remingchester Soooper Magnum" and you are all set. To paraphrase the ancient masters, "Hog wash!" It is true that at the higher impact velocities of rifle ammunition (2300-2700+ f/s), you get a larger temporary cavity, but not at the level one would expect from reading the magazine hype.
One big disadvantage in increasing bullet velocity is that bullets are designed to expand properly over a fairly narrow range of velocities. If driven too fast they "explode" on impact giving a shallow wound channel or if not fast enough they fail to expand and just punch a small hole. A superficial wound will most likely, as it will with a human antagonist hit with a weak pistol shot, simply make what you shot more aggressive or allow it to escape. Note that the new "all copper" rifle bullets now all the rage generally don't expand well below about 2000 f/s.
Even the ammunition manufacturers admit under close questioning and a couple of sips of their favorite spirits that the KE figures in their ballistics tables are there to impress the uninitiated and sell ammo (just like the pistol data.) . And impress them it can because KE is a factor of the square of the velocity, and as we all know, velocity sells now days--in spite of what we presented on the external ballistics link. Look at the table below. If we are to believe it, all we have to do is buy the latest big powder bottle and we are in business
|Velocity w/ 150 gr bullet||Kinetic Energy (ft lbs)|
Let's see now. A 150gr .30 caliber bullet at 2700 ± is generally considered suitable for game up to about 800 pounds by most authorities. The same bullet at 3500 out of the 300 Weatherby develops over 4000 ft lbs (which is fairly close to that of the .458 Winchester with a 500gr bullet which at 2000 f/s which produces about 4440 ft lbs.) Which do you want to have in your hands when that Cape Buffalo gets an attitude? To get even more absurd, theoretically one could drive a 55gr .22 caliber bullet to slightly over 5100 f/s and develop 3200 ft lbs of energy which some would have you believe makes it the equivalent of the .35 Wheelan with a 250gr bullet at 2400. Assuming you were sober which one would you want to use against an irate lion at 25 yards? Obviously kinetic energy isn't what we are looking for to quantify "more powerful."
It must be noted that kinetic energy does come into play with high velocity hard "penetrator" projectiles such as the "dart" rounds used in tank canon. There, the kinetic energy is used to literally burn through the target. I'll leave it to you to work out the KE of the M829 APFSDS-T (Armor Piercing Fin Stabilized Discarding Sabot-Tracer) 120mm round. It throws a 9.41 pound (that's 65,870 grains), 1.06" diameter, 31" long, depleted uranium dart at 5480 f/s from the 120mm M256 smooth-bore tank canon on the M1A1 and M1A2 tanks. You can think of it as a really big bore Remington "Accelerator" round. For those of you who left your calculators back at the office, see the footnote at the very bottom of this page for the answer, along with a picture of a "dart."
However, KE might, however, be able to serve as an index of effectiveness at different ranges when comparing the same bullet weight and diameter at different velocities.
We have seen on the external ballistics page that velocity doesn't have a tremendous effect on trajectory until the velocity change exceeds 200 f/s and even then the effect is really only noticeable at extreme range. It appears that the main effect of a velocity increase is to lengthen the range at which a given level of performance occurs (assuming the bullet construction cooperates). Just for grins lets assume that the given level of performance is the delivery of 1300 ft lbs of energy. (Yes, yes, I know... let's just assume and we'll also assume that we have a magic bullet that performs properly over a wide velocity range.)
In case you are wondering, I came up with this figure from Jeff Cooper's description of what the .308 Scout rifle was supposed to do--the taking of a target of up to 400kg (880 pounds), and his belief that 300 yards is the maximum range that one should attempt shots at game animals. (I have to agree with him because the average shooter can barely identify a target at 300 yards let alone hit it from field positions and in my experience an awful lot of folks can't consistently hit targets at 100.)
If we take 300 yards as the maximum "reasonable" range and assume using the same 150gr bullet as "standard" we come up with about 1300 ft lbs at 300 yards out of a 19" Scout so we'll use that as a standard of comparison. We'll launch a 150gr Hornady flat base from a.308 Scout, a .30-06, and a .300 Win Mag and look at the energy figures.
It would appear, if our assumption is correct, that all increasing MV by 300 f/s does is to extend the "equivalent effective range" by about 100 yards. Since 300 yards is about the most anyone should attempt a shot at, the whole thing kind of pales into insignificance. So the 300 Win Mag will do the same thing at 500 yards that the .308 will do at 300--Big deal! The target has to be hit first and I can count on the fingers of one hand the folks I know who can consistently hit with their first shot at 500 yards let alone those who know where their rifle shoots at that range. Besides you are burning 20-30 grains more powder just to get some meaningless increase.
Too many duffers believe the ad hype about the "magnums" and think that "more cartridge" will compensate for lack of marksmanship. In addition, all that powder going off causes faster erosion of the barrel's throat--not that many armchair hunters practice a lot with their rifles--and the increase in muzzle blast causes their already poor marksmanship to grow even worse. For the rare hunter or long range specialist who can make use of the slightly improved long range trajectory and power available from the big powder bottle rounds they may be of use. But for the "masses" I don't think so.
Ok, so we now know that upping velocity basically just extends the range at which a given level of performance occurs. The rest of the world needs something else to get more power.
If caliber remains the same, an increase in bullet weight increases what is known as sectional density which is basically the ratio of weight to impact area. (It also produces lower velocities in the same cartridge.) The main effect of bullet weight is to increase penetration (all else being equal) although there can be a slight increase in the expanded bullet's diameter (assuming it expands) since there is more material to work with. This can make it a more effective bullet assuming bullet construction is up to the task. While penetration is to be greatly desired it is not the only thing we want. If all we want is deep penetration we can just use fully jacketed or bullets with a hardened steel penetrator core and we'll be able to punch clear through most things. However, once again I don't think you would be too happy about facing an irate moose or a cape buffalo with an attitude, up close and personal with a .308 loaded with M62 AP ammo. However on larger thin skinned game (within reason) going to a heavier bullet in a given cartridge will give you some more penetration.
Below is a table of the sectional density for some common bullets weights and calibers. Note that as the caliber is increased the "standard" bullets become proportionally heavier.
Note the high sectional density for the 160gr .264 bullet. This is one reason why the 6.5 x 54 mm Mannlicher cartridge was so effective on big game. It drove deep and expanded well. The other effect of increasing bullet weight is to help increase the ballistic coefficient of the bullet. If the bullet shape stays constant increasing the weight can yield a slight trajectory effect at long ranges. We'll use the Hornady .30 caliber flat base bullets bullets as an example. (Data from Hornady.)
|Bullet Weight||Ballistic Coefficient (C1)|
However, remember that we have shown on the external ballistics page that a 15% change in BC at the same velocity has a negligible effect at reasonable ranges. We also saw on the external ballistics page a negligible change in useable trajectory with different bullet weights in the same cartridge if zeroed at the same range. It therefore appears that going to a heavier bullet in a given cartridge merely gives you some extra penetration (assuming proper and consistent bullet expansion).
More Bullet Weight and More Powder
Lets look at what we could do by using a bigger cartridge case with the same bullet diameter and burn more powder to launch a heavier bullet. All data based upon a 225 yd zero range with a 1.5" LOS. C1 ballistic coefficients are respectively .358, .431, and .485.
|.308 Scout / 150gr||.30-06 / 180gr||.300 Win Mag / 200gr|
Here we might be able to make an excuse for a bigger case in the same caliber. Raising the bullet weight and keeping velocity about the same or greater allows us to drive more mass deeper and in those cases of large thin-skinned game may give us the additional penetration and "umpf!" we are looking for when going after BIG thin skinned game. In addition, note that with the same zero range the trajectories are all very close until one gets out past 300 yards. Unfortunately, you will still generate a small wound channel and while it might suffice for docile targets we need to be able to cause a more certain reaction on targets that might decide to cop an attitude and attempt to ruin our big day in the field.
If you want a bigger hole, start with a bigger hole maker. As with the pistol, increasing the bullet diameter serves to increase the diameter of the permanent wound channel, which in and of itself is a "good thing," and it also, as a matter of course, increases bullet weight which helps to insure penetration.
Since it is apparent from previous investigations that, for the most part, simply jacking up the velocity does not make a particular cartridge more suitable for larger or more dangerous game, we may want to keep in mind that if we really need more power we really need to increase the bullet weight and also the bullet's diameter. This gives us more mass which is constant and a bigger permanent hole rather than velocity which is not constant. If you noticed in the sectional density table the "standard" bullets get proportionally heavier and heavier and for the most part have greater sectional density as caliber increases.
Notes from the field indicate that just as with the pistol, a bigger bullet has a greater effect on its target in the vast majority of cases. Deer usually fall faster when hit with a .35 than a .30, etc. given the same hit.
At this point I am sure that someone is asking, "How great an increase in caliber is needed to make a statistical difference?" That's a good question and as of yet I have not discovered an authoritative answer. I tend to think that a 25% to 50% increase in impact area is needed to be noticeably more effective but this theory is open for rebuttal. However, if one accepts that that .40 pistols are supposed to be noticeably more effective than the 9mms, one can look at the table below and see that a .40 cal has about 25% more area than a 9mm (.355"). Same thing with the .30 caliber rifles and the .35 caliber rifles, so perhaps there is something to this idea. One African hunter stated, when asked why he used a .600 Nitro double rifle, "Because they don't make a 700!" Nothing like a bigger hole!
|Caliber||Impact Area (inČ)||Caliber||Impact Area (inČ)|
An interesting inference can be drawn from the hunting regulations in African countries visited by hunters. They base their regulations not just on KE but also on bullet diameter. The following are taken from the regulations in place in Rhodesia. (Oops! I mean The People's Democratic Republic of Zimbabwe.)
Part A - Thick skinned, dangerous game [Buff,
elephant, hippo] requires a 9.3mm bullet (.362") or greater diameter bullet with not
less than 5.3 kilojoules (3,909 ft-lbs) muzzle energy; [Yes, I've noticed. Only a fool
hunts buff with a ".375." Maybe they are trying to kill off the Yankee tourists
but at least they realize you need some kind of a "real" gun for the bad boys!]
Part B - Thin skinned, dangerous and heavy game [eland, giraffe, lion] requires not less than 7mm (.275") diameter bullet with not less than 4.3 KJ (3,172 ft-lbs) muzzle energy;
Part C - General big game [up to wildebeest and zebra, say 600-800 lbs] requires not less than 7mm (.275") bullet diameter with not less than 3.0 KJ (2,213 ft-lbs) muzzle energy;
Part D - Light big game requires a bullet at least 5.6 mm (.220") and 850 Joules (627 ft-lbs) muzzle energy.
The inch/metric equivalents are theirs, using the English System of measuring bores.
One thing not touched upon in this discussion has been the effect of bullet construction. While this topic could take up several pages for discussion I think that it is safe to simply keep in mind that more weight or greater diameter will be useless if the bullet is not up to the intended task. A bullet that is too soft will open up too quickly and have reduced penetration or simply disintegrate on the target leaving you to face whatever it was you just shot with a serious reason to cause you harm. A bullet that is too strongly constructed may fail to expand at all. If it was originally of sufficient diameter this might not be too bad but if of a small initial diameter you may find yourself explaining your misdeeds to your target. Choose your bullets carefully.
My personal belief is if you have a rifle of a given caliber (say a .308 or .30-06), and you want (or need) something more powerful, what you need to do is to go up on either bullet diameter alone or bullet diameter and powder capacity and go to a .35 or so caliber. Don't waste your time burning more powder on a big bottle with the same bullet.
Of course, if you have lots of spare money and just have the need to have a whole bunch of different rifles to play with, be my guest. (...and you can send a couple to me so I can play too.)
I hope that the forgoing has provided some food for thought and I'm sure that I will be hearing from some of you. You can email your comments and ideas to me by clicking here
| Ballistics Main Page | Internal Ballistics Page | External Ballistics Page | Zeroing Page | Terminal Ballistics Page |
| Misc. Questions | Back to Fr. Frog's Home Page |
See below for the answer to the Penetrator KE math.
Answer to the KE calculations of the
M829 120mm Armor-Piercing Fin Stabilized Discarding Sabot with Tracer (APFSDS-T) round.
(Grid is approximately 4 cm)
Lets see now -- KE (ft lbs) = (W * VČ) / 450436. That gives us (65,870 * 5480 * 5480) / 450436 which boils down to (hold on to your hats!) 4,391,500 foot pounds (that's right 4.4 MILLION ft lbs). Sectional Density = W (in pounds)/DČ. That gives us 9.41 / .6 * .6 which equals 8.4. (That's eight point four--and you thought your 220gr .30 cal bullet had high sectional density at .343 (that's "point" 343.) The newer M829A3 round throws a 22.2 pound dart at 5200 f/s for 9.2 MILLION ft/lb.
As an interesting side note, when fired at 55 degree elevation, the A2 will travel 113,111 meters (123,630 yards or roughly 70 miles) and reach a height of 44,073 meters (48,171 yards or almost 27 miles). You are NOT safe if someone aims one of these at you. The accuracy of the dart is sub-MOA and the stated effective range is about 3000 meters (3270 yards). However, first round killing hits have been obtained out to about 6000 meters (6540 yards).
Sharp-eyed readers may note the 55 degree elevation for the maximum rage of this projectile. While spin stabilized cylindrical projectiles reach their maximum range in air at angles of between 25 and 35 degrees (45 degrees in a vacuum) the "dart is fin stabilized and not spun (the 120 mm gun is a smooth bore) and this gives it its maximum range at 55 degrees elevation--the fins keeping it point first through out its trajectory and providing some lift. Click here for a discussion of projectiles fired at extreme elevations.