Surface area on back end vs velocity

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outlawjw

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I know that if you have a 1" ram on a hydraulic cylinder with 1000 psi the ram will move at a given speed with a 500 lb load . If you truncate the fluid end of the ram giving to a 2" surface area then the ram will lift the same load at twice the speed producing 2000 lb of lift . Now my question is would a bullet be affected by increased surface area on tail end. I know oil doesn't compress & gas does but my knowledge falls off right there.
 
Pressure in a barrel pushing a bullet Peaks. It peaks at a near same distance in a given barrel. The bullet being pushed forward gains speed, but the pressure continues to fall off as the volume in the barrel increases.
Some assume bullet momentum is why that bullet gains speed. We do not know that for sure. You may try looking up pressure "curves".
Rear surface area has little effect inside that barrel. If there is any it would be small. Target shooters tend to like Flat based bullets assuming {And maybe right} that pressure is equal on the base of the bullet. Bullet base designs are more geared for what happens after it leaves that barrel rather then what happens inside the barrel.
As the Ram {as a rule} should maintain a constant pressure it would be wrong to compare the two.
Yet at the same time, a larger dia. bullet would create more pressure to some degree.
Lead bullets are soft enough this is usually not an issue. But then the hollow based bullets kind of mess up that idea. I learned about pressure curves when dealing with Black Powder.
The large caliber pellet rifles create a rather loud boom or should I say POP once that large pellet leaves that barrel. That would be the sudden vacuum created at the end of the barrel.
 
Yup bore. If not, then boat tailed bullets will shoot slower than flat bottomed bullets.

Your example is only half the story, you get double the force, but only half the speed. Just like pulley's, gears and other mechanical things, your 1" cylinder piston now needs double the movement to move the 2" section the same distance.
 
Some assume bullet momentum is why that bullet gains speed. We do not know that for sure...

Bullets can continue to gain speed even as pressure is dropping. I think. Moving peak pressure forward in the barrel seems to be a common theme for accuracy, but I know I get a lot of muzzle upset if the powder is too slow.
 
As long as pressure in the bore is enough to overcome the mass of the bullet plus its friction to the metal, the bullet will continue to accelerate. Once the pressure's dropped enough, the bullet will slow down.

A 230-gr. bullet from a .45 ACP case atop a few grains of Bullseye powder will drive it to maximum velocity in a barrel less than a foot in length. Same load in a 24 inch barrel ends up with a much lower velocity because the pressure's dropped too much to overcome bullet mass and friction. That same bullet in a .458 Win Mag case with a few dozen grains of a much slower powder will shoot it much slower that it does in a 5 inch barrel with that small charge of Bullseye, but with a much slower powder like IMR4198 or IMR4895, it'll leave much, much faster in that elephant rifle's 24 inch barrel.
 
Poor analogy.

The bullet isn't the ram in this equation, it's the load. The ram is the gas, created by the burning powder, producing the pressure, not the bullet, and as you said, gas is compressible, thus your ram is being compressed as the load is being pushed.
 
As long as pressure in the bore is enough to overcome the mass of the bullet plus its friction to the metal, the bullet will continue to accelerate. Once the pressure's dropped enough, the bullet will slow down...

I'm still scratching my head over this. I guess the key word is enough. But if the pressure drops only enough to allow a cushion of forward-moving gases to form around the projectile, it seems to me it'll really send it flying (pun intended).
 
The biggest problem with that comparison is, fluids will not compress while the air behind the bullet will. (over-simplified) That is what makes the outcome of hydrologic formulas predictable.
 
I'm still scratching my head over what this has to do with reloading. :confused:
 
Yes and No...

A long accepted belief is a the 'bigger' base of a bullet allowed more pressure (from the expanding gas) to be applied AND therefore the 'wider' projectile would go faster.

What I believe to be the current accepted belief of the same phenomenon is that of 'expansion ratio' - in that the volume of the expanded gases in a a larger diameter bore arm is greater, giving more thrust to the projectile.

However, this only applies when comparing two (or more) cartridges of the same case volume and bullet weight. One example which comes to mind is the comparison between the .30 Winchester Centerfire (usually called ".30-30") and the .32 Winchester Special cartridges. Both rounds use the same basic case, the same rifle (barrel lengths and maximum chamber pressure) and much the same bullet weights. However, the .30 caliber round is .308" and the .32 Winchester is .321".

With the same powder charge and the same bullet weight (commonly they both could be loaded with 150 and 170 grain bullets, the .32 was somewhat faster from the muzzle, but the .32 projectile had less sectional density and less ballistic coefficient; therefore the smaller bullet had greater range.

The only modern (all smokeless powder and high pressure loadings) I can think of currently would be the .300 and .375 H&H Magnums, except I'm not sure what weight bullet could be used in both. (Perhaps a 180 or 200 grain bullet is available for both calibers? I just don't see a 100 to 150 grain .375" bullet or a 300 grain .308" bullet as commercially available.) Having neither caliber, nor expecting to own such, I am not at liberty to do any testing.

Some enterprising soul might try a comparison of 'identical' barrels of calibers 9x19 and .30 Luger (one could find 100 grain bullets for both, I expect) in a Contender type frame. Again, I decline on grounds of just not interested enough.

In all, the advantages and disadvantages of 'larger' or 'smaller' bore diameters (with similar bullet weights) are discussable at length. In the past, calibers .303 British, 7.92mm Mauser, .30-40 Krag, .30-06 Springfield and 7.62x54R were similar enough to inspire arguments about which was 'best' for a specific purpose.

In a purely ballistic discussion, the science is well settled. In reality, no one shoots a purely ballistic rifle or handgun. Just remember to compare any fruit with another of the same fruit.

(By the way, in the argument of 'apples or oranges', I vastly prefer licorice.)
 
The bullet isn't the ram in this equation, it's the load. The ram is the gas, created by the burning powder, producing the pressure, not the bullet, and as you said, gas is compressible, thus your ram is being compressed as the load is being pushed.

I believe that the bullet would be the "piston" (which in this case does not have an attached ram as it does in a hydraulic system) ... the fluid in this case will be the expanding gas acts on the "piston" ... just as it does in an hydraulic system ... only there is no "end" or stop as in a hydraulic cylinder ...

And yes hydraulic "piston and ram" will shoot out of a cylinder just like a bullet does ... I've seen it happen and it is not pretty ...
 
First I am not talking about increasing bullet diameter , but increase surface area. Such as in a flat base has bore dia. Surface area & a boattail has a larger than bore dia. surface area. I guess I could find my answer in a reloading manual or with my crono by loading a fletbase & a boattail of same weight & shoot to see if there is a difference, if the bearing surface is the same length in both bullets .
Increasing the surface area on the bottom of the ram without increasing ram dia. does increase the speed of the lift because the flow is constant adjusted for the load on the motor ,& since power doubles with double the surface area then load on motor drops in half increasing speed of ram.
This is directly linked to reloading as a question of how to increase bullet speed without more powder.
 
Increasing the surface area on the bottom of the ram without increasing ram dia. does increase the speed of the lift because the flow is constant adjusted for the load on the motor ,& since power doubles with double the surface area then load on motor drops in half increasing speed of ram.

Do you mind posting something that even remotely support this "idea" ... because I believe you have something really mixed up as far as any of this on a rear of a bullet ...

Maybe a drawing or something to better show what you are talking about...
 
Given the same fluid pressure, doubling the ram diameter should quadruple the force, not double it. Surface area of a circle is pi times radius SQUARED. Pressure times area gets you force. And assuming the pump has the same pumping capacity, the 2" travel speed would be 1/4 that of the 1" ram. It is slower because it takes more fluid to fill the cavity for a given ram displacement.

The cross-sectional area of the bullet does have somewhat of a similar effect. You see this to some degree with .45 Colt Ruger loads compared to .44 magnum. The flipside though is that if you are increasing the diameter without increasing bullet weight, you are decreasing sectional density which relates to penetration and to ballistic coefficient.
 
outlawjw: Even if you created a hollow base in the bullet all the way to the nose of said bullet to increase the area to its maximum capability, the "ram" is still going to be at bullet dia. The cross sectional area of the bullet is all the gas has to act against. The shape is immaterial. Your hydraulic model is non-functional.

But hey, if hollow base wadcutters could prove your theory, they ought to be capable of Mach 4 with the same powder charge as a round nose with a flat base.

And while I'm no hydraulics expert, increasing the area of the piston will increase the force capability. It does nothing for ram speed at a given a pressure and flow. Increasing the flow rate will increase the speed. Nothing else.
 
First I am not talking about increasing bullet diameter , but increase surface area. Such as in a flat base has bore dia. Surface area & a boattail has a larger than bore dia. surface area.

The surface area of the boat tail exposed to the hot gases is greater than the surface area of a flat bottom bullet, but what's important is the surface area that adds to the force vector of the pressure. That would be the pressure pointing toward the front of the barrel. The additional surface area of a boattail bullet is radially inward. That does not add anything to the velocity of the bullet.

This is directly linked to reloading as a question of how to increase bullet speed without more powder.

The only way to increase bullet speed without increasing powder or weight of the bullet is to increase the pressure in the chamber. This can be done by seating the bullet deeper but in a rifle round, seating depth makes a proportionally small contribution to chamber pressure and an even smaller increase in muzzle velocity. For instance with a .308 typical load, seating the bullet from 0.1", 0.2" and 0.3" increases the Pmax by about 3,000 psi for every tenth of an inch and increases the muzzle velocity by about 40 fps for every tenth inch. Not worth the trouble.

If you want more velocity and are near the max load for a particular powder, you need to pick a different powder and use more. Typically you would look for a published load that uses a slower powder. You'll see that you would usually use a higher weight of that slower powder and the MV will be higher.

More speed is not the goal for optimum loads. You want to find the load that gives you the best accuracy while staying below the max and above the minimum velocity of your requirements.

The best way to test your particular theory is to simply buy a box of flat based bullets of a certain weight, a box of boat tail bullets of the same weight, load them with the same charge of powder and have at it with the chronograph.
 
Now my question is would a bullet be affected by increased surface area on tail end.
In the sense you are asking, no, as numerous posters have pointed out.
 
ArchangelCD,
Good point on fluids are not compressible. So I guess we are talking gas expansion laws here?
Anyway, good thread
 
Technically in physics, a gas is a fluid. Fluids comprise gases, liquids, and plasma.

Perhaps I misunderstood the initial question, but as has already been stated, increasing surface area by means if a boattail or a hollowbase will not help increase the forward force on the bullet. A boattail may aid slightly in reducing friction due to decreased bearing surface while a hollow base may do just the opposite, especially since the gases inside of the base cavity will be pushing the skirt of the bullet into the bore more forcefully which in turn would generate more friction.
 
Makes me long to be able to instrument each of these proposals to generate hard data.

Regardless, the bore cross sectional area is the key parameter here, as the force vector of the propelling gas is normal to the bore, along its axis. A flat-based projectile would have better opportunity to obturate and provide a more efficient seal and allow for less blow-by than a tapered base. As for hollow base designs, I suppose it depends upon how much of a radial component were generated, how thin the wall section was, and the angle of recess taper - the shallower the angle (draft), the smaller the radial component would be. In most cases I would suspect that the radial force component would be insignificant and much less than required to deflect the wall, but that's just a logical assumption on my part.

An interesting thought problem nonetheless. ;)
 
I am not much with phone use ability . So snap on applied hydrolics is a basic knowledge source . I have not been able to find our MSC book showing different brands & interior styles of rams , which is where I found the idea of changing the shape of the fluid side of the ram to increase power without increasing size.hop you can make this out
 

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