Pocket pistol loads

[Enthusiast]

I read about small single shot pocket pistols and how they were used for self defence in the Old West. I found a modern experiment measuring the power of these pistols, and surprinsingly a bigger load of gunpowder increased the velocity remarkably despite the barrel being very short. A 15 grain bp charge behind a .44 ball made a .44 hole in a watermelon, while a 40 grain charge blew it open. The barrel was I think just a little less than 3 inch long.

This made me wounder about the internal ballistics. I guess the explanation is that the bigger load had enough time to generate higher pressure before the ball had left the bore? If we take two .44 guns for example. One with a 4 inch barrel, loaded with 40 grains behind a single ball, and one with a 2.5 inch barrel loaded with 40 grains behind two balls. Which one will have highest velocity?

In a rifle same amount of powder and two balls means each has half as much potential energy as a single ball. But in this case I think a double ball load (or heavier bullet) will give the gunpowder more time to burn and time for pressure to build up, resulting in the two balls actually having higher velocity than a single ball would. What do you think?

[44 AMP]

Your concepts are flawed in several ways.

I found a modern experiment measuring the power of these pistols, and surprinsingly a bigger load of gunpowder increased the velocity remarkably despite the barrel being very short.

There is nothing surprising in this. Pressure is determined by gas volume, and gas volume is dependent on the amount of powder being burned.

Burning 40gr vs 15 will always result in more gas volume, which "pushes harder" on the bullet, in every barrel length.

With a short barrel you may not reach the full potential of the gas from a 40gr load but you will always have more pressure than the gas volume from a 15gr load. So, yes, the 40gr load launches the bullet faster than the 15gr load.

If we take two .44 guns for example. One with a 4 inch barrel, loaded with 40 grains behind a single ball, and one with a 2.5 inch barrel loaded with 40 grains behind two balls. Which one will have highest velocity?

The single ball will be faster. This is simple physics. A given mass, launched by a given pressure produces a given velocity. Double the mass (two balls) keep the powder change the same, and the lighter mass will be faster.

Black powder is not progressive burning the way modern smokeless powder is. Black powder burns very fast and is used up in a very short distance, its also not 100% clean burning. Even in long barrels there is considerable residue left in the barrel and "unburnt" powder ejected from the muzzle.

Longer barrel reduce the amount compared to short barrels, but its always there.

Really short barrel guns may even be blowing a considerable part of the powder charge out of the muzzle, in effect, wasting it.

But in this case I think a double ball load (or heavier bullet) will give the gunpowder more time to burn and time for pressure to build up, resulting in the two balls actually having higher velocity than a single ball would. What do you think?

Two balls will "give more time" because it is TWICE the mass, so acceleration is slower, and even with longer barrel time, top end velocity will be lower, because it is twice the mass.

The longer barrel time may give you results over half the speed of a single ball, but it will not match the speed of a single ball and cannot exceed the speed of a single ball using the same powder charge.

Simply, NOT HAPPENING...

Also, don't be mislead by calculated energy numbers. The formula for calculating energy is heavily weighted to favor velocity (velocity squared).

In simple terms, the reason the ball shattered the melon is because you drove it faster by using a much heavier charge of powder.