Amount of gas produced by different powders

[Resjudicata]

Does anyone know if there is a chart or information out there showing how much gas is produced by each of the different powders?

I think this would be a good thing to know for both comp'ed and non-comp'ed guns. The burn rate is helpful but I don't think it gives quite enough information. I would think that the amount of gas produced would probably also go along with amount of pressure made in the chamber. Also, the expanding gas pushing between the bullet leaving the barrel and the breach face is what operates the autos and what gives the recoil impulse I would think that a powder that produces more gas and higher pressures for a given PF would also produce more recoil.?.?

From looking at factory load data from Hodgdon comparing fast powders it seems that some produce quite different pressures from others at the same or similar power factor. I realize that burn rate can effect this too. But, it seems that for recoil control in a non-comp'ed gun the amount of gas produced would be a big factor in how the recoil feels.

Just wondering about it.

Chris

[XRe]

Amount of gas is directly proportional to the weight of the powder charge. These powders are essentially all made from the same few constituents (primarily, nitrocellulose, and sometimes nitroglycerin, plus a few additives) - there's no way to magically make more gas from the same stuff The differences between them are how they're cut/formed and treated to affect burn rate...

[Resjudicata]

Amount of gas is directly proportional to the weight of the powder charge. These powders are essentially all made from the same few constituents (primarily, nitrocellulose, and sometimes nitroglycerin, plus a few additives) - there's no way to magically make more gas from the same stuff The differences between them are how they're cut/formed and treated to affect burn rate...

Oh, okay. So, say for the sake of argument that 3N38 makes 1 cubic foot of gas per grain of powder. Then Clays would also make 1 cubic foot per grain of powder? (Regardless what the actual measurement is, it would make the same volume)

This is good to know.

Chris

[Pezco]

As a Chem-E. I don't believe it is that straight forward!

[CocoBolo]

As a Chem-E. I don't believe it is that straight forward!

+ 1 I just wish it was that simple. Burn rate is a good indicator but far from exact, two at near equal burn rates do not behave the same. I am a computer scientist and I could do the math if there were a direct relationship. I use T&E. (trial & error), and the worst of measuring devices the human.

[XRe]

+ 1 I just wish it was that simple. Burn rate is a good indicator but far from exact, two at near equal burn rates do not behave the same. I am a computer scientist and I could do the math if there were a direct relationship. I use T&E. (trial & error), and the worst of measuring devices the human.

Go read what I wrote again, and tell me where I mentioned burn rate having anything to do with volume of gas?

It's not a perfect conversion - if it was, you'd have a perfectly clean gun after every shot with just a light haze developing from whatever precipitates out of the gas. If the powder charge doesn't burn completely, some of the propellant weight will not contribute to gas volume (and no powder burns 100% efficiently). There are other minor effects, as well, but suffice it to say that, in general, mass of powder correlates directly to the mass of the ejecta (all the crap coming out of the barrel), the majority of which will be gas (because even inefficient loads tend to burn around 85%). There is more to it to compare mass of the gas to it's volume, but you can even demonstrate empirically that a heavier powder charge will generate a greater volume of gas using a camera and appropriate lighting so that you can see the gas...

There are other threads on the forum that discuss how the mass of the gas affects recoil energy (it most definitely does).

Res, because of efficiency, etc, you can't specifically make a blanket statement that 1 grain of any powder equals X cubic feet of gas (you also need to factor temperature and pressure in here, etc) - but I think you were getting at a more "gut feel" "amount of gas" instead of a literal measurement of volume displaced by the gas? If that's the case, your analogy is close enough for your purposes...

ETA - burn rate goes down a completely different rat hole... the burn rate charts have limited use, and their application to real world cartridge performance is dubious... They're trying to get across how quickly the powder converts to gas, basically - and that's dependent on a lot of factors. The quicker gas is created, the more quickly the pressure grows (until the bullet starts to move, where the pressure then starts to taper off). Frequently, the higher the pressure, the more quickly the powder burns, which then feeds back into the cycle, etc. That end of things is really complex, which is why Ron is saying you can't trust the burn rate chart He's spot on, there...

Edited May 6, 2010 by XRe

[MoNsTeR]

Assuming a complete burn, the mass of gas will be exactly equal to the mass of powder. The "volume" of gas is a bit of an error of thinking because gases expand to fill the volume available. This leaves pressure. There's no easy way to figure it but I would bet that between burn rate and possibly nitroglycerin content you can make a decent guess.

[CocoBolo]

Einstein's theory of relativity matter cannot be created or destoryed but it can be converted and that is the big got ya, what doesn't get converted to energy heat goes to ash and gas. So how much energy in the form of heat becomes yet another factor, we could go on an on with factors case volume, bullet weight, shape and size, tightness of the bore but the big limitation is the human subjective interpetation of recoil. So in the end its the worst measurement device that makes the call. If we were to rig the hand gun in a device to measure recoil and flip under controlled conditions and I have seen this done with rifles, the results of testing might just a lot different than current perceptions. I find this amazing we can disect the DNA of 2000 year old fossil but we still don't have a good handle evaluating a hand gun load.

In general non-compensated guns recoil less with a faster powder and a heavier bullet. In the end its finding the right combination that works for the shooter with the system aka the gun. Hence T&E becomes the method most widley used and accepted. Pressure is a factor and especailly when you have too much.

[Resjudicata]

I agree that the perceived recoil is less with a faster powder and heavier bullet. With a heavier bullet you use less powder for a given PF than you would with the same powder and lighter bullet. I have always worked under the assumption that with faster powder the powder stops burning and creating gas earlier than a slower powder. But, I think I'm wrong in that assumption. Now I wonder if it isn't just the amount of gas created regardless of how fast it's created that makes the fast powder/heavy bullet feel softer. Because with the faster powder you use less for a given power factor and thus create less gas volume or mass.

So, for you engineer type folks, what makes the pressure in the barrel? The volume of gas or the mass of the gas?

Also, does anyone know what components used in smokeless powder are converted more efficiently? Would a powder with more of the higher efficient components create more gas or do it quicker?

Thanks,

Chris

[Chills1994]

somebody up above left out noise. all that expanding gas sure does make a heckuva racket. so in effect noise = wasted energy....

should we just ASSume standard pressure/standard day...at sea level?

LOL!

oh...yeah...not all that powder does get burnt up and converted into a gas by the time it reaches the muzzle.

I think in the slow mo vids that were posted on the tripp research website you could see the "ejecta" leaving the muzzle. kinda neat.

anywhooo... i 'm still thinking thaT for now the good rule of thumb at least for open is to pick the slow burning powders....the ones with heavt charge weights. hs6 and ramshot silhouette come to mind.

[XRe]

Because with the faster powder you use less for a given power factor and thus create less gas volume or mass.

This. Realize that the gas and other ejecta are moving extremely quickly as they exit the muzzle. I've read everything from 5,000 to 10,000 fps... That's a large amount of energy in the equation. On another thread, I calculated out the difference between two .40 loads where the PF stayed the same (so, same bullet weight, same velocity), but you changed powders and had to use 1 grain more of the 2nd powder. I used the 5K fps number, and the calculation assumed 100% combustion (for sake of demonstration). It ended up having 10% more energy in the over all system!!! How much of that converts to felt recoil is hard to say, but you do notice it, obviously (all kinds of factors come into play, like weight of the gun, the recoil system, how you grip it, etc, etc). The calculation went something like this:

180gr @ 944 fps. 5.0gr powder. ( (180 * (944 * 944)) + (5 * (5000 * 5000)) ) = 285404480 <-- I have no idea what units this is...

180gr @ 944 fps. 6.0gr powder. ( (180 * (944 * 944)) + (6 * (5000 * 5000)) ) = 310404480

So, for you engineer type folks, what makes the pressure in the barrel? The volume of gas or the mass of the gas?

Both. V = nRT / p - where V is volume of the space the gas is contained in, "n" is the amount of substance of the gas (in moles), R is a constant, T is temperature, and p is pressure.

So, until the bullet starts to move, volume stays the same. If I increase the mass of the gas (through burning the powder), what has to happen to pressure to keep volume constant? It has to go up... As you can see, though, pressure will drop off dramatically as volume begins to increase unless we continue to create more gas.

Indeed, in a very fast burning powder, it has been either completely or largely converted to gas before the bullet even meets the lands in the barrel! This is why pressure can spike dramatically with a fast burning powder, especially if volume changes negatively (ie, bullet setback, for instance). Compare that to a very slow powder that requires pressure to combust completely, and that only ends up burning at, say, 85% efficiency (so, 15% of the powder charge ends up as solid ejecta, and never really becomes gas) - here, you're creating gas the whole time the bullet is in the barrel, and the pressure builds more gradually, as the powder burns more efficiently in a feedback cycle with pressure, but the volume is getting larger along the way, so the pressure never really spikes up the way it does in a a very fast powder load.

Also, does anyone know what components used in smokeless powder are converted more efficiently? Would a powder with more of the higher efficient components create more gas or do it quicker?

Both nitrocellulose and nitroglycerin burn rather well. The differences in the powders and their burn efficiency come back to the other factors - granule shape, additives to control the burn rate, etc. The "active" ingredients in most powders is exactly the same, otherwise. So, some of them have been tuned to release gas more quickly than others, etc. Efficiency, in the end, will depend upon the load and your gun - given enough barrel, most loads would probably burn with about the same efficiency, give or take. But, take a slow powder, and uncork the pressure before it's done burning (ie, say, with a shorter barrel), and reduce the efficiency...

You can't even say that a double base powder will liberate gas more quickly, because there are a number of relatively slow double base powders out there (again, additives, granule shape, etc). But, burn rate is trying to approximate your question about "quickness" - a faster powder converts to gas more quickly, is kind of the idea.

Take the energy equations above, though, and you find where the maxim about "heavy bullet / fast powder" for non-compensated guns comes in - lower total energy will reduce free recoil which will reduce perceived recoil. With an Open gun, you're try to use the energy in the ejecta to drive the gun down and forward, so you have an opposite desire - you'd like to drive that energy level up as much as is practical... So you go light bullet / slow powder, because a lighter bullet will require more powder to get to major PF velocity, and a slower powder will require a larger charge to push the bullet that fast. There's obvious tailoring to the gun, because not every comp is the same, and the presence of ports changes some things, etc. But that's the general gist...

[Resjudicata]

Learning is fun.

Chris

[MarkCO]

Having specialization in gas dynamics and combustion, I sugest you ought to listen to XRe. He definately has the right approach. While efficiency of the burn is a factor, if you have complete combustion, the MASS of gas generated IS related directly to the mass of the powder. Pv=nRT is the formula which gets you the understanding as to the actual volume. Since n and R are fixed (for a given mass) you can look at the direct correlation between Pressure, Volume and Temperature. Hope that helped some.

[GrumpyOne]

Because with the faster powder you use less for a given power factor and thus create less gas volume or mass.

This. Realize that the gas and other ejecta are moving extremely quickly as they exit the muzzle. I've read everything from 5,000 to 10,000 fps... That's a large amount of energy in the equation. On another thread, I calculated out the difference between two .40 loads where the PF stayed the same (so, same bullet weight, same velocity), but you changed powders and had to use 1 grain more of the 2nd powder. I used the 5K fps number, and the calculation assumed 100% combustion (for sake of demonstration). It ended up having 10% more energy in the over all system!!! How much of that converts to felt recoil is hard to say, but you do notice it, obviously (all kinds of factors come into play, like weight of the gun, the recoil system, how you grip it, etc, etc). The calculation went something like this:

180gr @ 944 fps. 5.0gr powder. ( (180 * (944 * 944)) + (5 * (5000 * 5000)) ) = 285404480 <-- I have no idea what units this is...

180gr @ 944 fps. 6.0gr powder. ( (180 * (944 * 944)) + (6 * (5000 * 5000)) ) = 310404480

So, for you engineer type folks, what makes the pressure in the barrel? The volume of gas or the mass of the gas?

Both. V = nRT / p - where V is volume of the space the gas is contained in, "n" is the amount of substance of the gas (in moles), R is a constant, T is temperature, and p is pressure.

So, until the bullet starts to move, volume stays the same. If I increase the mass of the gas (through burning the powder), what has to happen to pressure to keep volume constant? It has to go up... As you can see, though, pressure will drop off dramatically as volume begins to increase unless we continue to create more gas.

Indeed, in a very fast burning powder, it has been either completely or largely converted to gas before the bullet even meets the lands in the barrel! This is why pressure can spike dramatically with a fast burning powder, especially if volume changes negatively (ie, bullet setback, for instance). Compare that to a very slow powder that requires pressure to combust completely, and that only ends up burning at, say, 85% efficiency (so, 15% of the powder charge ends up as solid ejecta, and never really becomes gas) - here, you're creating gas the whole time the bullet is in the barrel, and the pressure builds more gradually, as the powder burns more efficiently in a feedback cycle with pressure, but the volume is getting larger along the way, so the pressure never really spikes up the way it does in a a very fast powder load.

Also, does anyone know what components used in smokeless powder are converted more efficiently? Would a powder with more of the higher efficient components create more gas or do it quicker?

Both nitrocellulose and nitroglycerin burn rather well. The differences in the powders and their burn efficiency come back to the other factors - granule shape, additives to control the burn rate, etc. The "active" ingredients in most powders is exactly the same, otherwise. So, some of them have been tuned to release gas more quickly than others, etc. Efficiency, in the end, will depend upon the load and your gun - given enough barrel, most loads would probably burn with about the same efficiency, give or take. But, take a slow powder, and uncork the pressure before it's done burning (ie, say, with a shorter barrel), and reduce the efficiency...

You can't even say that a double base powder will liberate gas more quickly, because there are a number of relatively slow double base powders out there (again, additives, granule shape, etc). But, burn rate is trying to approximate your question about "quickness" - a faster powder converts to gas more quickly, is kind of the idea.

Take the energy equations above, though, and you find where the maxim about "heavy bullet / fast powder" for non-compensated guns comes in - lower total energy will reduce free recoil which will reduce perceived recoil. With an Open gun, you're try to use the energy in the ejecta to drive the gun down and forward, so you have an opposite desire - you'd like to drive that energy level up as much as is practical... So you go light bullet / slow powder, because a lighter bullet will require more powder to get to major PF velocity, and a slower powder will require a larger charge to push the bullet that fast. There's obvious tailoring to the gun, because not every comp is the same, and the presence of ports changes some things, etc. But that's the general gist...

Thanks! That's clear as mud to me! You get my vote for the smartest person on here today!