In order to participate in the GunBroker Member forums, you must be logged in with your GunBroker.com account. Click the sign-in button at the top right of the forums page to get connected.
Bullet size - What is the difference??
famous wolf
Member Posts: 125 ✭✭
I am trying to understand the basis for bullet choices. For instance if you look at a ballistic chart at a 7mm-08 and look at a 120 and 140 Nosler Ballistic tip, the smaller bullet is faster, but the energy and trajectory at any given range is basically the same. So what difference does it make which I choose? If the bullet strikes the same place with the same engergy what is the difference??
Comments
Without getting into lots and lots of detail, you want to choose the bullet TYPE that is most suitable for your particular application.
For example if you are shooting a target competiton, you might want the most accurate bullet possible.
If you are hunting ELK you would want a bullet designed for that purpose. This is probably going to be a heavier-type bullet. A bullet designed to hunt SQUIRRELS (for example) probably wouldn't cut it!
Your particular rifle may well be more accurate with one bullet WEIGHT than another.
With respect to weight, in GENERAL, lighter bullets travel faster and therefore have flatter trajectories. They usually also have lower recoil.
On the other hand, in GENERAL, heavier bullets offer better penetration, and tend to retain energy better at distance. If you want to knock things over (eg like metallic plates), heavier bullets are better for that. As mentioned, heavier bullets tend to have more recoil.
Hope that helped a little.
Assuming we are talking about the same type of bullet.
If the 120 grain is travelling faster and the 140 grain slower, but at a given distance they impact the target generating the same energy, what is the difference?
I guess I should put it this way:
Assuming we are talking about the same type of bullet.
If the 120 grain is travelling faster and the 140 grain slower, but at a given distance they impact the target generating the same energy, what is the difference?
Again, they'll have different trajectories, since the lighter bullet will be travelling faster. The lighter bullet will also have less recoil.
One other factor you didn't consider is that even though bullet A and bullet B will have the same energies at distance "X", they probably will NOT have the same energies at distance "Y", with heavier bullets (in general) retaining energy better at longer distances.
But you are asking about what is usually called "terminal ballistics", ie what happens when the bullet strikes a target. So we have to go to physics 101.
Kinetic energy is a function of mass and the SQUARE of velocity (KE = 1/2 MV^2).
Meanwhile momentum (the IPSC shooters call this "power factor") is a function of the product of mass and velocity (momentum = MV).
Energy measures the ability of a moving object to do work (disrupting tissue is one possible example of "work" that a bullet could do). Momentum measures the ability of a moving object to transfer motion to a second object in impact. They are NOT quite the same thing.
So even though 120 grain bullet A and 140 grain bullet B may have identical KINETIC ENERGIES, the one with the higher MOMENTUM is going to hit "harder". That's going to be the heavier bullet. (Its also going to push harder against your shoulder when you shoot it for more recoil. . .there is no such thing as s free lunch).
With similar bullet construction, the HEAVIER bullet will also probably have more penetration, even if the energies are the same.
For example, if you look purely at ENERGY, 9mm luger and 45 ACP pistol rounds have the same energy. . .but the 45 ACP round fires a bullet twice as heavy and has more MOMENTUM. That's the round with more "power", and the one more likely to knock over a steel target, for example.
This is weight divided by crossectional area.
Generally, the greater the sectional density, the greater the penetration and the greater the retention of velocity & energy over distance.
Given equal energies at the target, the heavier bullet of the same caliber will penetrate deeper.
Shape is another important factor in bullet performance.
In addition to the learned replies above, bullets of different weight, but the same materials, will of necessity be of different shapes.
Agreeing with everything you said in this post, to be clear, bullets can have the exact same external dimensions, yet have different weights because they are made from different materials or alloys.
EG a bullet with a steel core will be lighter than an otherwise identical one with a lead core, and as you know there is some military type ammo that does use steel cores.
Likewise, bullets don't have to be solid, and there are bullet designs that have air cavities inside the bullet to affect weight and balance.
Its a little bit of a different thing, but bullets of different weights of the same material can also have similar profiles, with the heavier bullet just having a longer base.
To really strip this question down, assuming similar bullet designs and energies, the lighter 120 grain bullet will shoot flatter and have less recoil. The heavier 140 grain bullet will hit harder, but have more recoil and a less flat trajectory.
Obviously, the two rounds will have different trajectories, so a gun "zeroed" for one won't shoot to point of aim with the other, except at a particular distance where the two trajectories overlap.
In PRACTICE, with the average shooter using more "gun" than necessary and shooting only at close range, there may be NO functional difference between a 120 grain 7mm'08 and a comparable 140 grain one!
Your example of the 120 and 140 gr. Nosler BT's is a close one. The difference there is that at longer ranges the 140 will exceed what the 120 does. At shorter ranges the 120 will shoot flatter than the 140 as it is moving faster. Once it starts to slow down, it does so exponentially faster than the heavier bullet. Lighter bullets of equal/same form will tend to slow down faster than heavier ones. In this case the range that they are measured over isn't enough to show the differences.
The same comparison can't be made of two bullets of unequal form such as a RN and a VLD. An aerodynamically better, lighter VLD will continue on retaining speed much better than a heavier, RN bullet with poor aerodynamics.