Can someone please explain to my how it works that you get near same velocty in large caliber cartridges with lighter bullets than calibers like 300 win with much larger hulls

If I understand your question correctly, the answer is that the energy input to a projectile is directly proportional to the area of its base. A light weight, large bore projo will absorb more energy that a projo of the same weight in a smaller bore if the case size is the same and barrel length is the same.

You can get better performance in the smaller bore if you add more beans, ie, have a larger case capacity. Then, at some point, the larger case capacity will overcome the benefits of the larger bore area.

As a person who shoots both 9.2x62 and 300 magnums, let me say that I can only get a 250gr 9.3 bullet to shoot about 2500-2500fps. From a rifle with a similar barrel length, I can only get a 300 mag to shoot a 200gr bullet to 2900fps. They don't make 250gr bullets in 308 or 200gr bullets in 9.3. The performance of the two bullets I've reloaded are very consistent relative to their base area and weight.

I hope this hasn't confused you. Ku-dude

RWS makes (or made?) a 197gr. 9.3mm bullet. What about bearing surface of the bullet?

It is all to do with how much the gas is allowed to expand.

The best way to understand it is to first compare a small and large caliber on the same case capcity....say a 7mm Rem and 338 Win with equal length barrels.

In this case the internal volume of the 338 barrel is much larger, the powder charge and peak pressure are the same, so the gas gets to expand far more in the 338, that is, it gets to do more work. Thus a 338 can deliver far more kinetic energy to the bullet.

You can think of it like compression ratio in a car engine. If we have 13 to 1 ratio the gas gets to expand 13 times as opposed to 8 times with an 8 to 1 compression ratio.

Now if we ignored friction and made the 264 barrel long enough so that its internal volume was the same as say a 24 inch 338, then the 264 would develop the same energy as the 338 and therefore achieve equal velocity with equal bullet weights.

Now to your type of comparison, a good one would be the 30/06 and 257 Wby. In this case both deliver similar energy. The 257 Wby has more powder, but the smaller barrel volume means it does not get as much out of its 70 grain load as does the 30/06 from its 60 grain load. In other words the 30/06 is a small engine with a 13 to 1 compression ratio and the 257 isa big engine with an 8 to 1 compression ratio.

However, if you gave the 257 a barrel long enough to have the same internal volume as the 24 inch 30/06, then the 257 (ignoring friction) would deliver more energy than the 30/06 and therefore drive and equal weight bullet faster. In this case we have given the bigger engine the same compression ratio as the smaller engine.

While with equal pressure the 9.3 X 62 might be able to equal the kinetic energy of the 300 Win, the 300 Win will drive bullets of equal sectional density much faster or bullets of greater sectional desnity at the same speed.

Mike

[This message has been edited by Mike375 (edited 04-29-2002).]

Velocity is the result of pressure over time. The amount of pressure acting on a bullet of larger diameter is greater than on a smaller diameter bullet. With the same barrel time (bbl lenght)more energy is imparted to the larger diameter bullet. A easy way to view it is to take a pressure factor of 50,000 psi. If you have a bullet with a total base area of .5sq inch you will have 25,000 psi working on the bullet. If the area is reduced to .25 sq inch the pressure on the base drops to 12,500psi. Pressure remains the same -50,000 psi- but the amount acting on the bullet is different.
The bearing surface will play a small role as will the burn rate of the powder but like wgt bullets of larger cal fired at the same pressure from the same size case, ie 100 gr bullets from a 243 win / 308win, will always go faster.

Norma makes 232 grain bullets, and not bad ones. Try their Vulkan in 9.3 for deer or hogs. .30 cal 220 grs for comparison.

Don�t use the above mentioned bullet. The ~ 200 grs bullet is for 9.3x72R, a weak cartridge, weak bullet, dia is not totally correct, only usable for ROE deer ( max 30 kg, shot broadside ).

I would say velocity is not the same, but energy compares favourably. If you are a "momentum" type, the 9.3 gets even better. With the areodynamically best bullets downrange energy is also in the .300/.338 Win mag class.

But the drop is different: there is no such thing as a free lunch ...

Most people who know both state that the 9.3x62 "shoves" and is much nicer on the shoulder than the .300 Winnie, whic "kicks".

Good shooting! Hermann

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