Less pressure more velocity . . . ?

C

Curly T

Inactive
In a recent conversation an acquaintance mentioned switching to a different powder in his 6.5 x 284 than the brand he was using, according to him the new powder creates less pressure than his previous brand, but bullet velocity (with the same bullet as used before) was more.

Now my question is, is this possible?
And if so, how?
As one that often wonders what occurs inside the chamber, any opinion on the matter would be welcome.
Common sense tells me that for a given bullet to reach a given velocity in a given rifle, the pressure required to reach it must be the same, irrespective of the powder type.

Thanks!
 
Peak velocity is not always dependent on peak pressure, sometimes the pressure curve of the powder and the dwell of the pressure is what give the bullet it's velocity. A prime example is slower burning powders in handguns. They many times do not give any more peak pressure than faster burning powders, but give much higher velocities.
 
It's certainly possible because velocity is a function of average pressure, not peak pressure. The energy under the pressure vs time curve indicates bullet velocity. (Similarly, the area under the pressure vs distance (barrel length) curve represents the energy available to the bullet.) A powder that produces a lower peak for a longer time (may) have a larger total area, thus impart more energy/velocity to the bullet.
 
Buck460 and Brian nailed it. A slower burning powder would create lower peak pressure and could potentially produce more velocity.
 
A slower burning powder would create lower peak pressure and could potentially produce more velocity."

Roger that!
 
Yep. You'll notice that slower powders need heavier charge weights to reach a given velocity with a given bullet in a given gun than faster powders do. That heavier charge weight makes more total gas that keeps late barrel pressure higher out beyond the peak, and therefore a larger portion of the bullet's total acceleration happens after the peak with a slow powder than is the case with a fast one. Since two bullets going the same velocity have to have been subjected to the same average pressures over the length of the barrel, for the average pressure and final velocity to match when the powder creates higher muzzle pressure, if follows that the peak must have been lower.
 
Simply put a longer slower burn is (over the length of the bore) more thrust over a longer period. Think of it as a push instead of a whack. The peak, & the "time over half peak" curve is more thrust than a short sharp high pressure & waiting for the volume to decrease as the volume behind the bullet increases.

I use old stick (IMR3031) powder but can get both higher velocity & lower pressure by switching to a ball powder like H335.
 
The OP has been answered, but I think this can add to the conversation. Pressure is only useful in turning chemical energy into kinetic energy.

A bullet starts at rest and accelerates down the bore and out the muzzle. The total energy imparted is related to the AREA under the pressure curve for the time that the bullet is in the bore. So a higher peak pressure is meaningless unless it is also associated with more area under the total pressure curve.

Another way to think about it is the average pressure on the bullet during the time in bore. The higher the average the more acceleration the projectile will have on average. So a high peak pressure can have a lower average pressure than a slower burning powder that has a much smoother pressure curve.

You can say that the efficiency of a powder can be expressed in grains for velocity, but you can also measure efficiency in max pressure for velocity. If two powders produce the same velocity with different max pressure, the one with the lower max pressure could be "more efficient" for the cartridge. This of course ignores charge mass (or weight to be imprecise).

Jimro
 
Thanks!
Like I said, my knowledge of what happens inside the chamber and barrel, pressure wise, is quite limited.
Thanks for sharing your wisdom!
 
Kind of like the difference between punching something to move it, and pushing something to move it.
 
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