charge density

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watermelonman

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Anyone ever compare 3FG and 4FG power density in any scientifically significant way? I frequently read about people using 1.0-1.4g charges for compartments of the sizes I am using, but I am having more and more failures. My first thought was that measuring weight instead of volume should alleviate the difference, but now I am betting this is to blame for some incomplete separations.

That, or this Pioneer powder is simply wimpy. The gun guy says it is directly equivalent to black powder, though.
 
Black powder is always measured by volume.
The Pioneer powder is equivalent to black when used in a gun. Rocket ejection is not a gun.
Do a search of this site on using Pyrodex, typically needs more confinement than black

M
 
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+1 for more confinement.

Black powder substitute is very energetic - when properly confined. A centrifuge container tightly wrapped in a layer or two of vinyl electrical tape is an example of proper confinement.
 
There is no comparison.....BP is superior:)

It can be hard to find out here in CA, but I got some recently to supplement the ejection charge for my Warlock. Haven't used any yet. If a pound is 453 grams, then I think I might be able to kick a little bit Watermelonman's way. I don't want him having recovery issues --- I might be the idiot standing where the thing comes down!
 
Anyone ever compare 3FG and 4FG power density in any scientifically significant way? I frequently read about people using 1.0-1.4g charges for compartments of the sizes I am using, but I am having more and more failures. My first thought was that measuring weight instead of volume should alleviate the difference, but now I am betting this is to blame for some incomplete separations.

That, or this Pioneer powder is simply wimpy. The gun guy says it is directly equivalent to black powder, though.
Pioneer Powder is not Black Powder. It is a black powder substitute! For firearms! Only! https://www.americanpioneerpowder.com/

You will not find a single commercial solid hobby rocket motor that uses a black powder substitute as the ejection charge (or as a starter pellet). Why? Because they are not as reliable as black powder.

Black powder contains 3 chemicals: Saltpeter aka Potassium Nitrate as the oxidizer, charcoal as a carbon source fuel, and sulfur for ease of ignition. Black powder is a relatively low energy propellant because much of the combustion products are solids which provide no propulsive force. Potassium is hygroscopic and sucks water out of the air. Charcoal is easy to make however it make a lot of soot and smoke when it burns. Sulfur makes BP easy to ignite however it also makes sulfuric acid which is very corrosive. Also the potassium is converted to potassium hydroxide, a strong base which is also corrosive.

For all these reasons folks have looked for BP substitutes. The breakthrough was the discovery of gun cotton aka nitrocellulose aka smokeless powder aka single base. It is way more energetic than BP, makes only gaseous products and is harder to ignite so it is less sensitive and safer and is not hygroscopic so it does take up water and makes a lot less smoke. The problem is that smokeless powder generates a much higher pressure when confined than BP so BP firearms will explode if loaded with smokeless powder. The has brought about the development of black powder substitutes.

Black powder substitutes eliminate the sulfur so the corrosion from the hot gases is much reduces. In many cases the oxidizer is changed so that fewer solids are generated so potassium hydroxide is not generated and other solids are not generated so the burn is much cleaner and generates far less fouling than BP.

From a rocketry standpoint all BP and smokeless powders burn significantly slower than BP at atmospheric pressure so they generate gas at a slower rate. A reason why they burn slower is that they are harder to ignite and are likely to be pushed away from the hot flame front and not ignited at all.

This effect is minimal in a firearm where the powder is burned in a nominal constant volume container (the cartridge or gun breech). The burn rate is a function of pressure and temperature and both build up rapidly when confined in a firearm. This is not the case in a typical rocket recovery system where the powder burns unconfined under constant pressure. Here BP ignites and burns quickly where as black powder substitutes and smokeless powder don't. You will always experience some problems using anything other than BP in an unconfined burn for ejection purposes. That's a scientific fact due to kinetics, not a hobby myth.

Bob
 
Thanks Tony, that link is great! More thanks to Bob for the explanation, definitely not as happy with the Pioneer as I was when I walked out of the shop. ThirstyBarbarian, I will do my best not to hit you.
 
Thanks Tony, that link is great! More thanks to Bob for the explanation, definitely not as happy with the Pioneer as I was when I walked out of the shop. ThirstyBarbarian, I will do my best not to hit you.

I'll wear my horned safety helmet just in case.
 
There are a few who like the BP subsitutes for rocketry. However the vast majority (I believe) use real BP due to its ease of use. There are even one or two who from the sounds of it use pistol or shotgun smokeless powder. Black Powders are all pretty close to the same in burn rate when of the same grade (fg, ffg, fffg, ffffg) so one brand of BPs ffffg will be pretty close to another brands ffffg, there are differences that we as hobbyists will not likely see, BP rifle/pistol competitors on the other hand will, mostly related accuracy and cleanliness. Smokeless powders are not at all that similar, for one the names don't mean much, powders are commonly placed on a burn rate chart from fastest to slowest, here is an example of a burn rate chart https://www.reloadersnest.com/burnrates.asp. That being said BP requires a little confinement to burn properly, smokeless and BP subsitutes require quite a bit more. Notice that BP is not included on that list.
 
Black powder is always measured by volume.
The Pioneer powder is equivalent to black when used in a gun. Rocket ejection is not a gun.
Do a search of this site on using Pyrodex, typically needs more confinement than black

M


Black powder is measured by weight. It is usually purchased in one pound cans. Pounds, grains and grams are units of weight or mass. One grain equals the weight of one grain of barley if I am not mistaken. 7000 grains to a pound. 15.4 grains to a gram. Different BP granulation will yield different weights by volume. As will the same granulation by different manufacturers. BP charge measures, the brass or plastic tubes with marks on the sides to measure BP, does measure volume but it is calibrated to a certain weight of a consistent substance. Most are calibrated to the volume of grains (weight) of water, specific gravities and what not. The 100 tick mark will be 100 grains (weight) of water. Water will yield the same weight per volume consistently, BP will not. That is especially true for larger granulation. Measures from different manufacturers are different as well.

4f will weigh more than 3f of the same volume because it is a smaller granulation and more dense. 4f burns faster and is more energetic than 3f, resulting in higher pressure. In a gun, you pack the powder down with a ramrod anyway, so original measured volume would be meaningless as it changes when packed, the weight stays the same. Yeah a rocket is not a gun but that doesn't change grain and grams to volume instead of weight.

Volume is measured with milliliters or cubic something. Nowhere will you find a volume measurement of grain or gram. A grain is a grain and a gram is a gram no matter what you are measuring. What weights more, 100 grams of aluminum or 100 grams of lead? Neither. Which occupies the most space? The aluminum, it is less dense. 1 cubic inch of aluminum weighs 682.5 grains. Lead is 2870 grains.

What sort of device are you guys using to measure the "volume" of your BP?

This is why BP is not measured by volume: https://www.skylighter.com/fireworks/help/Black_Powder_Size_Charts.asp There is quite a bit of variation in the sizes of the grains.

To the OP, here is video showing side by side reactions from different grain sizes. Not really the scientific answer you were looking for, but it will give you an idea of how much more energetic 4f is than 3f. You will notice he uses a scale to measure the BP, not the cup he has it in. Then you will see how much more dense the finer grain powder is, even if it weighs the same.
[video=youtube;WcVlc2m4a1s]https://www.youtube.com/watch?v=WcVlc2m4a1s[/video]

You simply cannot accurately measure black powder by volume.

Mike
 
Mike, in the shooting sports that use bp(muzzleloading/bp cartridge) the measures used are marked in grains which when used with FFG will yield the approx weight in grains with about +-10% depending on the manufacturer of the measure and your bp brand/batch. Most loading manuals specify the charge by volume and granulation as well. Performance of black powder has much more variation than smokeless powders from batch to batch, so measuring by weight from batch to batch won't necessarily yield the same amount of gas generation either. Because there is so much variation in mfg/batch the actual pinpoint grain weight is not as meaningful as in smokeless loads. In muzzleloading and bp cartridge we typically use a volume measure from charge to charge, not weight and have found consistent accuracy/point of impact. You set your charge for the approx grain setting, adjust for point of impact/accuracy and then throw a consistent volume after that. If you have a new batch/brand it is prudent to verify your measure, whether weight or volume is still giving you what you want. Swiss FFFG for example typically gives higher velocities at the same charges than Goex.

However at the small amounts we use for ejection charges, the difference is probably irrelevent when measured by weight or volume. Once you have the amount you want for your ejection charge, it is just as good if not better to just consistently use a volume measure for your bp. Of course that has to be set for the granulation you are using, you can't swap FFG or FFFG for an FFFFG volume and expect the same result. You need to test or have some sort of starting point for the granulation/powder type to evaluate what you need for the volume you are trying to eject. Any exact weights given are only as good as that powder brand/granulation/batch. A rule of thumb of 1.3 grams of FFFG may be good for most brands/batches in 4" airframes and typical volumes you need to pressurize...overkill for most, underkill for some.

Smokeless powder is much more consistent from batch to batch and can yield excellent/better accuracy using weight measure, but most rifle/pistol loads after initial adjustment are thrown by volume because the extra time to throw charges by weight are normally only a benefit in extreme accuracy/long range. This is true even in match pistol loads where you are weighing 1.9-2.7 grain charges.

Frank

Black powder is measured by weight. It is usually purchased in one pound cans. Pounds, grains and grams are units of weight or mass. One grain equals the weight of one grain of barley if I am not mistaken. 7000 grains to a pound. 15.4 grains to a gram. Different BP granulation will yield different weights by volume. As will the same granulation by different manufacturers. BP charge measures, the brass or plastic tubes with marks on the sides to measure BP, does measure volume but it is calibrated to a certain weight of a consistent substance. Most are calibrated to the volume of grains (weight) of water, specific gravities and what not. The 100 tick mark will be 100 grains (weight) of water. Water will yield the same weight per volume consistently, BP will not. That is especially true for larger granulation. Measures from different manufacturers are different as well.

4f will weigh more than 3f of the same volume because it is a smaller granulation and more dense. 4f burns faster and is more energetic than 3f, resulting in higher pressure. In a gun, you pack the powder down with a ramrod anyway, so original measured volume would be meaningless as it changes when packed, the weight stays the same. Yeah a rocket is not a gun but that doesn't change grain and grams to volume instead of weight.

Volume is measured with milliliters or cubic something. Nowhere will you find a volume measurement of grain or gram. A grain is a grain and a gram is a gram no matter what you are measuring. What weights more, 100 grams of aluminum or 100 grams of lead? Neither. Which occupies the most space? The aluminum, it is less dense. 1 cubic inch of aluminum weighs 682.5 grains. Lead is 2870 grains.

What sort of device are you guys using to measure the "volume" of your BP?

This is why BP is not measured by volume: https://www.skylighter.com/fireworks/help/Black_Powder_Size_Charts.asp There is quite a bit of variation in the sizes of the grains.

To the OP, here is video showing side by side reactions from different grain sizes. Not really the scientific answer you were looking for, but it will give you an idea of how much more energetic 4f is than 3f. You will notice he uses a scale to measure the BP, not the cup he has it in. Then you will see how much more dense the finer grain powder is, even if it weighs the same.
[video=youtube;WcVlc2m4a1s]https://www.youtube.com/watch?v=WcVlc2m4a1s[/video]

You simply cannot accurately measure black powder by volume.

Mike
 
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Compression of the BP also makes for more consistency from shot to shot in BP cartridge/muzzleloading rifles, in rockets the tighter we compress the BP the more completely the charge burns.
 
Hate to point this out, but few black powder enthusiasts take their scale into the field. ALL of the ones I have seen measure their gun loads be volume. Now there may be some who take a small scale out and weight each shot worth, but I haven't seen any.

Having said that, the ones I have known always use the same granulation size every time. They also shook their powder between loads to ensure it wasn't packed down.

In my rockets, I have always just poured some into the ejection charge well. I can say that in the few HO launches I have done, I haven't weighed the amount of powder used.

Kirk
 
This is a debate probably as old as powder measures themselves.

We are on the same page just seeing it differently. The measures are marked in grains as you say. Grain is a unit of weight. The measures are calibrated using weight, same with tabletop reloaders. When I shot primitive, we would weigh our BP and make our own measures to throw the same weight. Using my progressive reloader for shotguns I would weigh a few of the charges it threw and hone in on the correct weight and check periodically. We simply use devices to throw charges of a certain weight.

And as you say, in such small amounts the difference is nearly insignificant.

No matter how you look at it, the fact is grain and gram are units of weight. If BP was measured by volume it would be written in cc, ml, or cubic inch, not grains or grams.
 
This is a debate probably as old as powder measures themselves.

We are on the same page just seeing it differently. The measures are marked in grains as you say. Grain is a unit of weight. The measures are calibrated using weight, same with tabletop reloaders. When I shot primitive, we would weigh our BP and make our own measures to throw the same weight. Using my progressive reloader for shotguns I would weigh a few of the charges it threw and hone in on the correct weight and check periodically. We simply use devices to throw charges of a certain weight.

And as you say, in such small amounts the difference is nearly insignificant.

No matter how you look at it, the fact is grain and gram are units of weight. If BP was measured by volume it would be written in cc, ml, or cubic inch, not grains or grams.

Oh, I think the real confusion and reason for the question was in the gun shop telling me Pioneer powder was black powder and was not pyrodex. It may not be pyrodex, but it is definitely not black powder either.
 
Pyrodex is both a brand name and a generic name for similar products, it is getting to the point that if you walk into some places selling (like Sportsmans Warehouse local to me, or other large outdoor sporting goods stores) black powder substitutes the people who work in those departments don't know what they are talking about. They just know that "pyrodex" and black powder do approximately the same thing under the same conditions in a firearm.
 
Oh, I think the real confusion and reason for the question was in the gun shop telling me Pioneer powder was black powder and was not pyrodex. It may not be pyrodex, but it is definitely not black powder either.

Pyrodex is both a brand name and a generic name for similar products, it is getting to the point that if you walk into some places selling (like Sportsmans Warehouse local to me, or other large outdoor sporting goods stores) black powder substitutes the people who work in those departments don't know what they are talking about. They just know that "pyrodex" and black powder do approximately the same thing under the same conditions in a firearm.
A bit of background information.

Black powder is the generic name for a compounded solid propellant made from salt peter (potassium nitrate), charcoal and sulfur. The 3 materials were commonly available 1000 years ago when black powder was first compounded. Salt peter provides the oxygen and charcoal is the primary fuel and sulfur is a secondary fuel that greatly increases the ignitibility. Compounding BP is inherently dangerous and explosions and fatalities are not uncommon. Most major fireworks families have a fatal compounding explosion every decade or two because they compound by hand, and they are the professionals so it's really not wise for amateurs to make it. BP has many drawbacks as an efficient propellant as a large fraction of the combustion products are solids that contribute to gun fouling and corrosive depots and not to propulsive gas generation. About 150 years ago, nitrocellulose aka gun cotton aka smokeless powder was invented and rapidly replace black powder in firearms. Smokeless powder is more energetic and develops much higher breech pressure and does not generate corrosive byproducts so it is still used in most firearms today, however it is dangerous to use in firearms designed for black powder because the firearms can blowup due to excessive breech pressure. Black powder substitutes were developed to eliminate the problems associated with BP: low efficiency, lots of smoke, breech and barrel foulding and corrosion. Black powder substitutes remove the sulfur and reduce or eliminate the salt peter by substituting other oxidizers to get rid of the solid combustion products that cause fouling and corrosion. Several of the first to gain public acceptance are the trademarked (not generic names) Pyrodex(R) and Triple7(R) black powder substitutes. Other black powders use organic acids such as ascorbic acid as the oxidizer, and Pioneer(R) powder is one of these Trademarked black powder substitutes.

About 500 years ago, black powder firearms began to appear commonly replacing the bow and arrow for the military and hunting. When you are out in the field, you can not weigh powder so you had a powder horn that would dispense a relatively standard volume quantity of BP to reliably fire a relatively standardize ball projectile from a relatively standardize bore in a firearm. As BP quality became better and more standard, and cartridges were loaded in factories, the BP powder densities and grain sizes were industrially standardized and the volumes and weights were calibrated to efficiently and reliably reload firearms and cartridges with BP.

All black powder substitutes are more energetic than black powder but not as energetic as smokeless powder, so the BP substitute weight is less than that of BP, but greater than smokeless powder. In the 20th century when black powder substitutes were developed, the substitute black powder densities were adjusted to utilize standard black powder measures use in the field to reload BP firearms, so for shooting purposes you can interchangeably use equal volumes of BP substitutes for BP in modern BP weapons, however this equivalency does not apply for rocketry use where the combustion occurs near atmospheric pressure versus the 1000 atmosphere pressure in a BP gun breech. If you use the same methodology in rocketry, the likelihood is the descent time will be approximately equal to the ascent time, making your pride and joy into an expensive single use disposable rocket.......

Bob
 
Quick question:

Has anybody ever tried grinding rocket candy into a powder and using that as an ejection charge? Are the burn rates vastly different from BP?
 
I frequent pyro forums and have seen many accidents, most of it from making black powder. Either it went off while emptying the mill, or in one case a guy had the mill jar explode in his hands when he shook it. The stuff ignites very easily.

I'm not sure when Blackhorn 209 was invented but people have said they are smokeless powder that was modified to work with standard bp volume measure (and also at pressures that bp firearms can handle). There are many configuration of smokeless powder out there and if carefully done, they can be made to shoot at relatively low pressures. Shotguns use smokeless powder and they are low pressure. The big problem is there's a lot of idiots out there, and that many bp firearms have absolutely no proof requirements (compared to standard firearms) so they're made of softer steel. If a bp firearm is made with the same standard as a standard firearm, then it can safely handle smokeless. However you must measure it by weight and NOT use standard bp volume measure (this has blown up a few smokeless capable guns such as Savage ML-10II).

If you can make smokeless work for rocketry applications I think they will actually work better. For one thing you will use a lot less powder due to its efficiency, but also the powder will produce next to no spark and therefore you have less risk of burning parachutes.
 
I frequent pyro forums and have seen many accidents, most of it from making black powder. Either it went off while emptying the mill, or in one case a guy had the mill jar explode in his hands when he shook it. The stuff ignites very easily.

I'm not sure when Blackhorn 209 was invented but people have said they are smokeless powder that was modified to work with standard bp volume measure (and also at pressures that bp firearms can handle). There are many configuration of smokeless powder out there and if carefully done, they can be made to shoot at relatively low pressures. Shotguns use smokeless powder and they are low pressure. The big problem is there's a lot of idiots out there, and that many bp firearms have absolutely no proof requirements (compared to standard firearms) so they're made of softer steel. If a bp firearm is made with the same standard as a standard firearm, then it can safely handle smokeless. However you must measure it by weight and NOT use standard bp volume measure (this has blown up a few smokeless capable guns such as Savage ML-10II).

If you can make smokeless work for rocketry applications I think they will actually work better. For one thing you will use a lot less powder due to its efficiency, but also the powder will produce next to no spark and therefore you have less risk of burning parachutes.

I have one of those high-tech automatic powder scales for reloading ammunition. Repeated many times in the instructions is the warning to NEVER use the scale to measure Black Powder or Black Powder Substitutes as doing so can cause ignition of the powder inside the scale with disastrous results (the hopper can hold around a pound of powder).

It's one of the rules I refuse to break :)
 
I wouldn't break that rule either. A pound of black powder going off in my face is going to ruin my day for sure. At least smokeless powder won't do much if it went off because most the powder would be blown off
 
I have one of those high-tech automatic powder scales for reloading ammunition. Repeated many times in the instructions is the warning to NEVER use the scale to measure Black Powder or Black Powder Substitutes as doing so can cause ignition of the powder inside the scale with disastrous results (the hopper can hold around a pound of powder).

It's one of the rules I refuse to break :)

I wouldn't break that rule either. A pound of black powder going off in my face is going to ruin my day for sure. At least smokeless powder won't do much if it went off because most the powder would be blown off
That's because the automatic screw feeders in the automated smokeless powder weighing measures could create enough friction/pressure to ignite the much more sensitive black powder and most black powder substitutes. Not good!

The traditional way to reload BP and BP substitute cartridges is to calibrate a throw volume for the weight of the throw, and that's the traditional way to reload smokeless cartridges as well. For a given can of powder it is easy to calibrate a throw volume to a powder weight. It's always been done that way. The issue that causes some non-repeatability is the filling of the throw volume with the same quantity of powder. The automated smokeless weighing dispensers quote a +/-0.1 grain error, and the volumetric ones typically have +/-0.2 grains or so do to slightly different filling factors from shot to shot.

Bob
 
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