Confused.

[Echo9]

If you add more mass to the bullet, you get a higher sectional density, which should yield better penetration -- but this also decreases velocity, which reduces penetration.

If you lower the grain, you get a faster bullet, but less mass yields lower sectional density, and so, less penetration. I don't get it.

Does it seem to anyone else that all these different bullets do the same damn thing? How is one to determine what effect different changes to grain, velocity, etc, will have on external/terminal ballistics?

Also, recoil -- as I understand it, recoil is the conservation of linear momentum. MV^2. So why does everyone say increasing bullet weight increases recoil? Shouldn't reducing bullet weight have the same effect if recoil is mass x velocity?

 

[LAK]

Heavier bullets with higher sectional density will penetrate better in soft tissue. Even at significantly less velocity than lighter bullets at higher velocity. This is just the laws of physics and the nature of soft tissue; a high fluid percentage in composition.

Drop a large heavy elongated stone into water "nose first", held at arms length above the surface. Take a smaller round stone and toss it up high so it falls far enough before striking the surface to gain some real "velocity". The larger stone will tend to "slip into" the water whereas the smaller one "smacks" the surface. The incompressibility of liquids tends to resist impacts and reduces velociy in a shorter distance with the lighter projectile which lacks the momentum of the heavier one.

Not very scientific but the best way I can explain it.

Lighter bullets at higher velocity will in general tend to penetrate hard materials better. Velocity seems to be a major factor in breaking down harder materials, thus a regular full metal jacket bullet - thin gilding metal jacket and lead core - in a small caliber round such as .223 will penetrate a surprising thickness of steel plate. Whereas a .357 magnum bullet weighing almost three times as much but at half the velocity will not penetrate as well against steel plate.

These are not absolutes as it also depends on bullet design and materials.

Recoil is based largely on action and reaction. And weight of bullet is not the whole story. Weight of powder charge figures in, as much of it is pushed down the barrel behind the bullet.

A heavier gun means more inertia for the recoil energy to move. Thus a heavier gun means less recoil in general.

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Je Suis Prest

 

[Laserslug]

The conservation of momentum and the conservation of energy both are true.
momentum = mv
energy = 1/2 m (v squared) + heat + work
for momentum:
mass of bullet * velocity of bullet = mass of gun * velocity of gun
10g * 2000 feet per sec = 1000g * 20 feet per second

So if the gun is made twice as heavy, the gun velocity decreases to 10 feet per second when recoil starts.

 

[Echo9]

Just realized my OP says MV^2 for momentum. Sorry about that.

If momentum is mass times velocity, and lowering your grain makes a lighter bullet that has more velocity, it seems like going to a lower grain should increase recoil.

 

[Sky]

actually Newton had something to say about mass and velocity. More mass means more force which brings into play opposite equal force..... recoil. Shot gun, same powder, but different pellets or slugs will give more recoil as the pellet weight increases very slight but it is there.... well my opinion anyway hahahaha

 

[Freedom_fighter_in_IL]

Echo, everyone is always stating Newton's 3rd law but most seem to overlook the second law, which applies directly to firearms. Have a quick study of it and the little light above your head will light up!

 

[bhk]

This fast/light bullet vs slow/ heavy bullet effectiveness has been going of for generations. I am over sixty and have reading arguements about this since I was 10, and some of that writing was done decades before that (O'Conner vs. Keith).

What I have learned through experience and mucho reading is that light/fast can result in lightening kills on lighter game. Lighter bullets often have lighter construction, resulting in the rapid/explosive expansion that helps promote these rapid kills. Penetration will depend on bullet construction, but will generally not be great due to the designs often used for these fast bullets. The heavy/slow crowd will argue that their bullet construction promotes more controlled expansion, more momentum, and much more penetration making the heavy/slows more suitable for larger game such as bear, moose, and elk. The muzzle energy may be the same, but the results can be much different. Bullet construction itself can be a make it or break it decision regardless of which approach you take. Some fast/light situations can be fair penetrators if used with a bullet of tough construction.

Other issues enter into this argument, such as bullet trajectory. One could argue forever whether the 30-06 or the 45-70 is a better elk killer, but one cannot argue which one has the flatter trajectory, making long shots easier to make. These discussions always make a hunting camp a lively place to be. If there was a perfect choice, we would all be using it. How boring would that be!!!

 

[Laserslug]

Pressure

The acceleration of the bullet in the barrel is from Newton's second law.
f=ma
so acceleration is force divided by mass.
The force is due to the pressure of expanding gases.
The pressure is force per square inch , (force per area).
A bigger bullet has more square inches, so the force is greater for bigger bullets.

The volume of a bullet goes up faster than the cross-sectional area of a bullet as caliber increases, so bigger bullets accelerate more slowly than small bullets using the same gunpowder. That slower acceleration means the big bullets have a slow speed.

 

[gunguru]

Everyone is over complicating the way you look at this issue. I'm no mathmatician, but think of it this way. Throw a baseball at a brick wall and say the ball was traveling 70 mph., it bounces back and does not penetrate. now imagine a vehicle traveling 70 mph. at the same wall. The Greater the mass of the object the more stored energy it has when traveling at speed, increase the mass and you increase the amount of stored energy it can carry for longer distances. which is why larger calibers can kill further out. More energy transferred into a bullet and the amount it can store means that when that bullet is stopped it dumps that energy into the object that stopped it.
Now for the other recoil question. think of it this way, you shoot a weapon and the bullet exits the barrel right?, hopefully. The force pushing your bullet out is also pushing back at the gun also. When you lighten the load the force of pressure has to push on to get your bullet out, it lightens the load it pushes back on your gun. Less energy transferred into your bullet to get it to boogie out of the tube, the less is transferred back into your shoulder. the effect of upping the weight of the bullet also makes the pressure increase, your shoulder will feel the increase. The consequence of increasing the weight of the bullet is that the bullet is unable to gain speed as quickly wich equals more time to transffer energy. You can figure the equations out, i got a headache just reading your posts.
How does the posi-track on a Plymouth work?.... It just does.

 

[DaveBeal]

I did just some basic physics and came to an interesting conclusion. All other things being equal, the muzzle energy of a given cartridge in a given gun is independent of the bullet weight. However, the muzzle momentum, and therefore the recoil, is proportional to the square root of the bullet weight. So a heavier bullet will cause more recoil.

I assumed that the propellant gas obeys the ideal gas law (PV=nRT) and that the temperature of the gas remains constant as the bullet moves down the barrel. I also assumed that the powder is completely and instantaneously converted to gas when the gun fires (not realistic, but any other assumption would put the calculation beyond my meager abilities.) This implies that the pressure (and therefore force) on the bullet is inversely proportional to the distance from its base to the breech of the chamber.

Since energy is force times (or integrated over) distance, the muzzle energy of the bullet is the force applied to it by the propellant gas integrated over the length of its travel down the barrel. If you plug in the expression for pressure described above and do the integration, you find that the muzzle energy depends on the length of the barrel, the initial pressure produced by the powder and the bullet's cross-sectional area, but doesn't depend on the bullet's weight. Then, by using the definitions of kinetic energy, momentum and a little algebra, the muzzle momentum comes out to be proportional to the square root of the bullet weight. So, for instance, if you increase the bullet weight by 20% and keep everything else the same, the recoil should increase by about 9.5%.

 

[jmr40]

No one is taking bullet design into consideration. Expanding bullets expand more rapidly at higher velocity. This often leads to equal bullet weights that will penetrate much more when they are moving SLOWER.

This is commonly observed when hunting. Not at all unusual to see a 150 gr 30-30 bullet at 2000 fps penetrate further on game animals than the same bullet fired at 3300 fps from a 300 magnum.

 

[Freedom_fighter_in_IL]

Well DaveBeal, in basic theory you are a little bit right. You have to also take into account that a bullet actually stops at least 2 times upon ignition. First stop is upon the ignition of the primer. This starts the bullet moving till it hits the lands. Then you have first ignition of the charge. This scoots the bullet up until it gets out of the throat and into the tighter dimensions of the barrel. Pressure then builds up yet again until it starts the bullet along it's path out of the barrel. Lots of things going on in that few nanoseconds that are directly related to pressure but not so much related to recoil.