Velocity limit of black powder

Gunpowders have a maximum velocity obtainable because they have to push the weight of their own combustion products down the barrel along with the projectile, so even with the lightest bullet possible, the velocity will be limited. With smokeless powders this limit seems to be under 5,000 FPS. Parker Ackley invested a lot of time and money trying to get to 5,000 FPS and probably didn't make it. I say probably because he used a ballistic pendulum to measure muzzle velocity, an imperfect instrument at best.

After a debate about Civil War sniping, I looked up the velocities quoted for replica muzzle loading rifles. A little over 2,100 FPS seemed to be top. I would guess that the velocity limit would be lower than smokless simply because the lower pressure gas has to push all the solid particles in the smoke ahead of it. Threads about black powder cartridges are vague about velocity. BTW, I am referring to real block powder, not one of the substitutes.

Bill

There's also the idea the gas can't expand any faster than the speed of sound in it. So the hotter the better, which is where smokeless has an advantage.

wesg said:

There's also the idea the gas can't expand any faster than the speed of sound in it. So the hotter the better, which is where smokeless has an advantage.

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The "speed of sound limit" theory has been "dis-proven" by the efforts of interested air gunner's. I believe the record at present is over 1800 fps. But of course, the question remains about the temperature of the propelling air. After all, the velocity of the molecules is averaged. some are at zero, and some are going very fast. Which are driving the projectile?

For shitz and giggles, look into "light air guns" The velocities obtained are truly amazing. 'set your nose crooked' . ;-)

9100 said:

Gunpowders have a maximum velocity obtainable because they have to push the weight of their own combustion products down the barrel along with the projectile, so even with the lightest bullet possible, the velocity will be limited. With smokeless powders this limit seems to be under 5,000 FPS. Parker Ackley invested a lot of time and money trying to get to 5,000 FPS and probably didn't make it. I say probably because he used a ballistic pendulum to measure muzzle velocity, an imperfect instrument at best.

After a debate about Civil War sniping, I looked up the velocities quoted for replica muzzle loading rifles. A little over 2,100 FPS seemed to be top. I would guess that the velocity limit would be lower than smokless simply because the lower pressure gas has to push all the solid particles in the smoke ahead of it. Threads about black powder cartridges are vague about velocity. BTW, I am referring to real block powder, not one of the substitutes.

Bill

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(Successful) 'sniping', even if we presume long(er) distances, mostly, did not/does not require uber-velocity, nor uber-flat trajectory.

What it requires most of all is repeatable predictability. Sufficient retained energy as well. 1860's heavy, but VERY well stabilized projectile was the precision rifleman's tool. The counter to it was more likely to be cannon and canister shot as counter snipers.

With repeatability, one can make use of skill/instruments/both to gauge and adjust for flight time, winds, ground level and aloft [1], Earth's rotation, etc.

ABSENT predictability, velocity alone cannot help.

Those among our predecessors as sought 'the limits' were also among the first to back down FROM them a notch or three and work in a more practical and repeatable comfort zone.

Bill

[1] More than one of the "Project HARP" tubes achieved muzzle velocities in excess of 7,000 FPS. Artillery, 'Naval Rifle', and tank main-gun, not shoulder-fired, 'sniping' , AKA "first round hit or take the consequences" is a first-order coondingie tightener, but in the interests of accuracy, (and tube life..) generally worked at somewhat lower velocities.

There are a number of ways to produce hypervelocities and Gerald Bull probably tried most of them. The question wasn't about them or even black powder snipers, but about the propagation velocity of standard black powder.

Actually, Mach 1 airflow isn't hard to achieve. Things like vortex tubes reach it internally at a relatively low air pressure. I have made torches that have shock lines in front of their nozzles. The issue is whether black powder can push all those particles faster.

Bill

A little off the mark, but this is worth looking at
Smooth Bore Cannon Ballistics

3 mile limit....;-)

Check out the velocities of the Paris Gun.

They got to 5,400 FPS, but the Paris guns had booster charges that lit off as the projectile passed them. It is doubtful that they could have reached that velocity with a single charge in the breech. You probably could exceed that velocity by attaching a charge to the projectile, making a gun/rocket hybrid. A typical space rocket uses most of its fuel adding kinetic energy to the remaining fuel so it continues to accelerate, reaching speeds higher than the basic exhaust velocity of the rocket engine. The best ones also use LH/LOX, wh ich has a combustion product molecular weight of 18 (H2O, water), which produces a much higher exhaust velocity that normal gun powders.

Of course, none of this uses black powder.

This does bring up an ancillary question. Our little space effort, Gateway Space Transport, now defunct, used a jet engine fueled by normal kerosene and kerosene/LOX rockets. It occurs to me that we could have used hydrogen for the jet fuel and LH/LOX rockets for a considerable gain. The normal immediate reaction would be that hydrogen would burn up the jet engine, but not so, you would only feed enough hydrogen to reach the rated exhaust temperature.

There is a story around that Gary Powers' U2 ran out of LH used to boost his engines, making him fly lower, within SAM range.

BTW, does anyone need a Turbomeca Marbore IIA jet engine? I have a nice one for sale.

Bill

The Paris gun did not have booster charges.

Wouldn't this be the same as calculating hydraulics? So for instance you would use the chamber surface area as one piston area, and the area of the base of the bullet as the other piston? Then calculate for force? Then the bullet velocity would be calculated for acceleration based on mass and force applied. So the limit wouldn't be the expansion rate of the gas, rather the volume of the chamber vs. the bore diameter.

Forestgnome said:

Wouldn't this be the same as calculating hydraulics? So for instance you would use the chamber surface area as one piston area, and the area of the base of the bullet as the other piston? Then calculate for force? Then the bullet velocity would be calculated for acceleration based on mass and force applied. So the limit wouldn't be the expansion rate of the gas, rather the volume of the chamber vs. the bore diameter.

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Simple math? Yes. Up until the point that the surface that is under pressure is receding at a rate faster than the arriving (expanding) gas molecules.

Pressure ( acceleration/ velocity) can come from many combinations of momentum transfer.

CalG said:

Simple math? Yes. Up until the point that the surface that is under pressure is receding at a rate faster than the arriving (expanding) gas molecules.

Pressure ( acceleration/ velocity) can come from many combinations of momentum transfer.

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I didn't mean to say calculating the acceleration would be simple, however the greater the ratio of chamber volume to barrel volume, the less effect on pressure there would be due to the bullet travelling down the barrel. At some point the theoretical pressure peak would be post bullet exit as the chamber volume is increased.

On this side topic..... I've asked the question on other forums. Has anyone come across a comparative chart of various smokeless powders and their gas generation "factors"? Vihta Vuori publishes such data for their own powders, but make no comparisons to others. Burn rate comparison charts are quite common. Even if they may be the same data rehashed and reprinted. I've seen some confusing listings for H335...;-)

9100 said:

Our little space effort, Gateway Space Transport, now defunct, used a jet engine fueled by normal kerosene and kerosene/LOX rockets. It occurs to me that we could have used hydrogen for the jet fuel and LH/LOX rockets for a considerable gain.

There is a story around that Gary Powers' U2 ran out of LH used to boost his engines, making him fly lower, within SAM range.


Bill

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The trouble with LH, as I understand it, is that while it has a good energy to mass ratio, it's energy to volume ratio is poor. Requires huge tanks, very well insulated.

Space Shuttle external tank - Wikipedia, the free encyclopedia

Vs a kerosene fueled system:

S-IC - Wikipedia, the free encyclopedia

E.F. Thumann said:

The Paris gun did not have booster charges.

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I could have sworn that I read a description of booster charges on the Paris guns, but it appears not. They were used on the V3 in WWII. The search also turned up this paper describing projectiles with propellants in their bases, the gun/rocket hybrid I mentioned earlier.

http://www.dtic.mil/dtic/tr/fulltext/u2/a203307.pdf

The paper comments on the problem with simply increasing the charge- the extra energy needed to force the combustion products down the barrel, which was the starting point of the thread. Eventually you will reach a point where additional gunpowder doesn't increase projectile velocity.

Re the larger volume of LH, you do have to drag along a much larger tank. A carbon atom attaching to two oxygen atoms yields about the same amount of energy as four hydrogens reacting with two oxygens, but the combustion product of carbon, CO2, has a molecular weight of 44 while the hydrogen product is H2O, water, with a weight of 18. That makes a huge difference in the thrust produced and hydrogen powering a jet engine would get a lot more thrust per pound of takeoff weight since it doesn't have to schlep along its oxygen supply. Burning hydrogen gives the same amount of energy as three times the weight of carbon. When you get into VTOL vehicles, the difference in performance would be spectacular.

Bill

I've often wondered about this as well. The German WW2 V weapon used a multitude of side chambers, and I wonder what kind of limit one might reach with that using BP.

I also wonder if Gerald Bull experimented with that concept using smokeless.

I also wondered about gun shells, shells with loaded charges and projectiles that would fire just outside the muzzle of the larger gun, and I suppose even a third gun would be possible, the inverse of tree stage rocket engines, the first large gun shoots the smaller gun, which doubles it's velocity because it's moving already, and the third shell gun benefits from the velocities imparted by the other two. These things actually make sense in rarefied atmospheres and space.

Above a certain velocity a round pellet explodes into a gas plasma with fantastic results. I've seen photos of dust particle impacts on the surface of aluminum (I think) at tens of thousands of miles per hour, they can hurtle along for millennia holding their velocity, crossing vast distances in space. The same particle accelerated to such velocities in our atmosphere would become harmless quickly.

I understand the new rail guns achieve very high velocities with finned projectiles, and the smoothbore Rheinmetall 120 MM tank gun reaches 5700 FPS maximum. (I wonder how they do that)

For sniping I always thought a long boatail should be pretty predictable at BP velocities, but there is more time for variables to effect them, including time for the target to move.

BTW, about the Paris gun, long ago I read that the turntable needed 8" hardened steel balls to roll on, and they bought them secretly in the USA. The Paris gun put first man made objects in the stratosphere.

9100 said:

They got to 5,400 FPS, but the Paris guns had booster charges that lit off as the projectile passed them. It is doubtful that they could have reached that velocity with a single charge in the breech. You probably could exceed that velocity by attaching a charge to the projectile, making a gun/rocket hybrid. A typical space rocket uses most of its fuel adding kinetic energy to the remaining fuel so it continues to accelerate, reaching speeds higher than the basic exhaust velocity of the rocket engine. The best ones also use LH/LOX, wh ich has a combustion product molecular weight of 18 (H2O, water), which produces a much higher exhaust velocity that normal gun powders.

Of course, none of this uses black powder.

This does bring up an ancillary question. Our little space effort, Gateway Space Transport, now defunct, used a jet engine fueled by normal kerosene and kerosene/LOX rockets. It occurs to me that we could have used hydrogen for the jet fuel and LH/LOX rockets for a considerable gain. The normal immediate reaction would be that hydrogen would burn up the jet engine, but not so, you would only feed enough hydrogen to reach the rated exhaust temperature.

There is a story around that Gary Powers' U2 ran out of LH used to boost his engines, making him fly lower, within SAM range.

BTW, does anyone need a Turbomeca Marbore IIA jet engine? I have a nice one for sale.

Bill

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You need to do some research........before you post. Lol

jabezkin said:

You need to do some research........before you post. Lol

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In what respect? I am certain I saw a statement that the Paris gun had boosters many years ago, long before the internet. I have followed firearms for 68 years and have only found the one paper I referenced about traveling charges, although I knew it was possible. The rest of my statements are correct. I only said there was a story extant about the U2.

Bill

do some research

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Or better yet, don't read such thought provoking threads.

After searching for an hour for data on the Paris gun turntable's 8" diameter American made ball bearings (96 for each turntable) I found very little, so I spent next weeks grocery money on a book about it. It could have been worse, had I purchased the Paris gun book written by two scientists, including GV Bull (Yep, one and the same), it would have cost a couple weeks worth of vittles. My wife doesn't understand the buying of books.

Very interesting thread I say because I've often wondered why large bores were used for sniping during the civil war (The war of Southern aggression. ) I hadn't ever considered that there was a limit to the velocity potential of black powder.

The answering post mentioning the higher heat of smokeless gasses rings true, because with out the heat of millions of degrees a thermonuclear explosion couldn't happen, it's the super rapid expansion of those millions of degrees heat to the air around the blast that causes blast damage I believe.
A hint lies in Diesels computations for thermal efficiency of his engine, the heat being held at the flame temperature during expansion by controlled addition of fuel during the power stroke.

So, as to black powder velocities, I wonder if anyone ever tried carrying the charge with the projectile so that freshly burning gasses are added to the column at the projectile end instead of the breech end where it has to push that long column of gas? Said moving cartridge might separate at the muzzle. The aim here is maximum velocity, not accuracy. (Gyrojet, but it did not use pressure but thrust instead.)
Just wondering.
parts

... I wonder if anyone ever tried carrying the charge with the projectile ...

Once again you run into the problem of accelerating the powder gas although in this case, the powder is still solid. I am not in a position to do the math on this (have forgotten most of the calculus I learned 50 years ago) and that is what would be needed, along with some burn rate data and other things.