Basics of powder burn rates and useage

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locknloader

New member
Can anyone shed some light on the basics of powder burn rates and how that comes into play when reloading (or point me to some good reading on the subject).

The very basic understanding i have so far is that fast burning powders reach peak pressure more quickly, have more of a "snap" than "push" recoil feel.

I am having a hard time finding some good information about how burn rate comes into play when selecting a powder for a given round. I have only been finding general statements like "dont use a fast powder, pressure jumps too quickly" or people will just randomly suggest a powder, then when i look it up i notice the burn rate is damn close to the one someone else said not to use, -CENSORED--CENSORED--CENSORED-!!!

I'd like to have a good enough understanding of the critical data points of a powder so i can apply that towards load development, and not use general statements made by others to guide my decision.

I am mainly interested in 9mm and 40cal right now, but i think it's necessary to include other rounds like 45 in the discussion because i believe that's a lower pressure round and the 9/40 are higher pressure ones?

Sorry for my ignorance but gota start somewhere!
 
I am seeing that bigger bullets like slower powders and that for higher peak velocities slower powders are also used. Plinking loads are often better with faster powders as the charges are smaller. Really slow powders do seem to have more felt recoil except Superformance, which is a blended powder, that produces highest velocities with remarkably less felt recoil. I am finding that the suggested most accurate powders for a given bullet weight are usually the best choice.
 
If you assume two powders have the same energy content per grain and they differ only in burn rate, the basic idea is that it will take a larger quantity of the slower burning powder to have enough burning to generate enough gas to reach the same peak pressure in the same amount of bullet travel down the bore. In other words, if the bullet base is, say, one inch into the bore at the pressure peak in both instances, you will need to have a larger quantity of the slower powder burning for that slower burn rate to have generated an equal volume of gas to that of the faster powder, and therefore make equal pressure. The larger quantity of powder keeps burning, and by the time the bullet reaches the muzzle it has made a larger total amount of gas than the smaller charger of faster powder does. That means the pressure drop by the time the bullet gets to the barrel is less. That means the average pressure past the peak was higher (unless the barrel is extremely short), and thus the bullet is going faster. So the slower powder lets you get to higher velocity without increasing the peak pressure back closer to the breech end of the gun.

The slow powder advantage for velocity has some practical costs. More powder costs more money, obviously. The larger charge increases recoil both by the added effort to move the mass of the gas down the tube and by the higher muzzle pressure increasing "rocket effect" when the bullet exits the muzzle. The slower powders need higher pressure to burn efficiently, so you are more limited in load range and lighter bullets don't give them enough inertial resistance to build pressure against, so they aren't for them, either. They expose a rifle throat to higher temperature longer, so they tend to erode it more quickly.
 
I don't feel that it is a good idea to use burn rate charts to select a powder. There are too many factors that affect the actual burn rate, which is determined by "closed bomb" tests by the manufacturer. Much better to simply know where the powder lies in the chart in relation to others, then use only proven load data for the one in question. GW
 
Here is a brief overview of smokeless powder and how different burn rates apply to different loads be they shotgun, pistol and rifle. Other similar papers on the subject can be found using Google. Something else to consider with powders is their temperature stability over a range of temperatures. Will my loads behave on a cold day of 20 F as they will at 90 F in the hot sun?

Member Slamfire has endless pages of research on powders including their burn rates, temperature sensitivity and also longevity verse storage time and conditions. Hopefully he will wander along with some advice and thoughts. There are more characteristics of powder to consider when choosing a powder for a specific application but a few are covered in the above link.

Wow, with my slow typing I see already more post have been added. :)

Ron
 
Can anyone shed some light on the basics of powder burn rates and how that comes into play when reloading (or point me to some good reading on the subject).
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You really need to read a good reloading manual before you go any further. I highly recommend the Lyman 49th Edition, although I believe Lyman has a 50th Edition Reloading Manual now in print.

Don
 
I prefer to use light charges of fast powder for plinking and target loads, and powders in the middle of the spectrum for medium strength loads. I usually don't load full strength loads but, i'd choose slower powder for that application. I like the Lyman manual because it lists the powders in order of burn rate and identifies which load was the most accurate.

I don't get too wrapped up in burn rates and will sometimes experiment with various other combinations than those listed above. You also have to remember that burn rates don't always fall neatly in order. Depending on the cartridge, powders can leap frog one another due to other characteristics and make-up of the powder.

Also you can't rely on everything you read online. Just because some random poster says not to use a powder in a cartridge doesn't mean anything. I'd wager to guess that 1/4th of posters in reloading forums don't have a clue what they are talking about. Follow your reloading manuals not internet posts.
 
locknloader - What are you looking for exactly?

The big issue with "burn-rate" and powder charts, with respect to load development, in general, is that they are extremely rough lists of powder which, under certain circumstances only, exhaust their energy from faster to slower. What they don't provide are the parameters of the conditions during measurement, relative quantitative measurements, nor which powders are identical. So, a burn rate list is really all but useless for any serious development.

Powder burning characteristics can vary depending on the conditions with which they are burned [different chambers, barrel length, bore diameter, etc.] But, generally speaking, you are looking for a powder, that will hit it's energy peak, just as the bullet exits the muzzle.

With respect to fast powders being "snappy" and slow powder providing "push." Recoil is dependent on bullet weight, muzzle velocity and firearm weight/design. Powder selection simply determines velocity.

I'm with Don [USSR] - you need to do some reading of published material on the subject before you start "experimenting."
 
Northof50 said:
Powder burning characteristics can vary depending on the conditions with which they are burned [different chambers, barrel length, bore diameter, etc.] But, generally speaking, you are looking for a powder, that will hit it's energy peak, just as the bullet exits the muzzle.

With respect to fast powders being "snappy" and slow powder providing "push." Recoil is dependent on bullet weight, muzzle velocity and firearm weight/design. Powder selection simply determines velocity.
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What does the text in bold mean? Can you give an example?


With respect to recoil, the amount of powder required to reach a given speed affects recoil as well, as this is part of the formula for calculating recoil force.
 
74A95 - No. I cannot give you a specific example, as I do not have the equipment to measure such a parameter.

But, theoretically, when a bullet seals the bore, the case expands and seal the chamber, the powder burns, producing energy [gas -creating pressure and heat], ideally, you want the pressure created to be at its peak just as the bullet is leaving the muzzle. For example, if too little powder is used and you get a squib load [bullet stuck in barrel] the powder's energy was exhausted before the bullet could leave the barrel - hence the bullet stops accelerating and comes to a stop due to friction. A powder that is too slow, will not produce adequate energy to produce optimum velocities. An example would be using H110 in a 9mm. You could fill the case. But, because the powder burns much slower, you can never get peak performance. But, put the same H110 in a 44mag and the burning characteristics [due to chamber size, friction, bullet weight, etc] change.

Developing loads, is complicated without proper equipment. When I state "develop loads," I do not mean picking various suggested powder from a manual. I am referring to developing loads for wildcat cartridges or for blending different powders in a single cartridge. That's why I simply use referenced information from published manuals. My conclusion is the load that produces the highest velocities listed in the manual, are those powder that are generally providing optimal burning characteristics and is usually a good powder to start development. From there, I go to those powders suggested that produce similar velocities. For what it's worth.

Yes. Powder affects velocity not felt "snappiness." IMO
 
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Northof50 said:
74A95 - No. I cannot give you a specific example, as I do not have the equipment to measure such a parameter.

But, theoretically, when a bullet seals the bore, the case expands and seal the chamber, the powder burns, producing energy [gas -creating pressure and heat], ideally, you want the pressure created to be at its peak just as the bullet is leaving the muzzle. For example, if too little powder is used and you get a squib load [bullet stuck in barrel] the powder's energy was exhausted before the bullet could leave the barrel - hence the bullet stops accelerating and comes to a stop due to friction. A powder that is too slow, will not produce adequate energy to produce optimum velocities. An example would be using H110 in a 9mm. You could fill the case. But, because the powder burns much slower, you can never get peak performance. But, put the same H110 in a 44mag and the burning characteristics [due to chamber size, friction, bullet weight, etc] change.
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That's not how it works. Peak chamber pressure occurs long before that, after the bullet has moved about a quarter-inch or half-inch. By the time the bullet leaves the barrel the pressure is a fraction of peak chamber pressure.

Here's a pressure curve for a 38 Super. http://www.shootingtimes.com/files/2014/04/Figure-5-compensators-Pressure-or-Gas.jpg Pressure peaks when the bullet is at the 1" mark, and given the length of the cartridge taking up a good portion of that length (the pressure curve starts at about 0.7").
 
74A95 - Sorry, that graph does not dispute what I wrote. It simply displays information on 1 particular chamber without reference to the amount of powder, bullet weight. It is an "out of context" picture.
 
74A95 - I re-read what I wrote and realize I misused "pressure" instead of "energy" of the powder. Chamber pressure is highest in the beginning because of the size of the chamber created is smaller than when the bullet is at the end of the barrel. As the bullet leaves the barrel, the chamber becomes larger, hence the chamber pressure is lowered. But, that's different than the energy of the propellent.
 
74A95:
What does the text in bold mean? Can you give an example?

Below is a typical rifle type pressure curve.
Pressure%20Curve.png


The above image is taken from here which is a pretty good read on the resulting pressure curves when powder burns.

Worth noting is how the leading edge of the curve makes for a fast rise as the pressure peaks and the trailing edge as the pressure slowly decreases and finally the bullet exits the barrel. The link explains how different powders and barrel lengths figure into the scheme. Also of interest is how fast the pressure builds, drops and bullet exit. The entire show is over in about 1.1 mSec in this typical example which in seconds is 0.0011 second.

As to recoil Hatcher's Notes has a section devoted to how recoil is calculated as well as a SAAMI white paper on the calculations. What is interesting is there are a number of online recoil calculators and if you enter the same data into several you get several different numbers out. :)

Ron
 
Reloadron said:
As to recoil Hatcher's Notes has a section devoted to how recoil is calculated as well as a SAAMI white paper on the calculations. What is interesting is there are a number of online recoil calculators and if you enter the same data into several you get several different numbers out. :)

Ron
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The different results is a result of deciding what 'speed' to attribute to the escaping gas. Opinions vary, with some using a preset, such as 4000 fps, while others prefer a ratio of the bullet exit speed, such as 1.25, 1.5, 1.75. There is some discussion of that here: http://kwk.us/recoil.html
 
CAUTION: The following post includes loading data beyond or not covered by currently published maximums for this cartridge. USE AT YOUR OWN RISK. Neither the writer, The Firing Line, nor the staff of TFL assume any liability for any damage or injury resulting from use of this information.


Pressure reaches its peak in the first couple or three inches of bullet travel, even in a high power rifle. You can tell this is so because that is where copper fouling is heaviest, out in front of the throat. It is caused by the high acceleration at the peak upsetting the bullet outward against the bore, causing friction with the bore to be highest at that point. The bullet usually picks up a third to half its velocity by the time the peak starts falling off. That results in the bullet going so fast down the rest of the bore that expansion, which is the growth in the volume of the space the powder is burning in due to the added volume of bore behind the bullet, that the powder no longer makes gas fast enough to keep up with that expansion.

Below is a QuickLOAD double trace of typical bullet position vs. pressure. To exaggerate, the green dashed line is a very fast powder (Bullseye; note that this load is just a model and would be too irregular to be trusted in a real gun: DO NOT USE IT!), while the latter is a much slower one (Varget). The charge weights are adjusted to achieve the same peak pressure. Note the 18.8-grain Bullseye charge (green dashed line) peaks at about half an inch of bullet travel, while the 45.5-grain Varget load peak about an inch and a half forward. Despite that slower start, the Varget holds the barrel pressure up behind the bullet longer. That results in higher velocity—about 2700 fps vs only 2150 fps for the Bullseye load. Slow powders keep the pressure from falling off quite as rapidly because of the greater amount of gas their larger charges make, but it's still typically a good deal of drop from the peak pressure value.

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Moreover, you wouldn't want high power rifle peak pressures present at the muzzle. Experiments have been done from F.W. Mann forward to show that if a bullet exits at the peak of a rifle's pressure, the bullet is then generally distorted by the high pressure muzzle blast, which, even if it occurred perfectly uniformly, would greatly reduce the bullet's ballistic coefficient.

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As to burn rates for loads, you will find no two load charts seem to agree, if they are from different sources. This is because it is expensive to do the standard test and manufacturer's don't share their results. So the charts are assembled on guestimates from the velocities produced by various charge weights. You can expect that any powder manufacturer's burn rate chart will have its own powders in the right order, but the others in it may be off.

One of the reasons for the above is powder, even in an approximating model like QuickLOAD, will have about eight different characteristics that describe its behavior. You could, for example, have two powders of the same burn rate with with significantly different energy content, as with a double-base vs. a single-base powder in the same range, and the double-base will produce more velocity.

Evaluation of a powder's suitability for an application then is generally judged by a number called its Ballistic Efficiency. This is the percent of the stored energy in the powder that is converted to kinetic energy in the bullet, the rest being lost to propelling the powder and its gas or else being converted to heat in the gun. Each cartridge shape tends to have its own best efficiency and velocity compromise. It changes with cartridge geometry. Some short straight wall pistol cases can get surprisingly close to 50% BE. A .30-06 is typically just below 30. Some of the overbore cartridges can get down into the teens.

Some burn rate charts group powders on the same line because they tend to be useful in the same cartridge and bullet weight combinations. That is a better way, IMHO, to go about organizing one for a handloader to refer to. Lapua and Western do this.
 

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"The different results is a result of deciding what 'speed' to attribute to the escaping gas. Opinions vary, with some using a preset, such as 4000 fps, while others prefer a ratio of the bullet exit speed, such as 1.25, 1.5, 1.75. There is some discussion of that here: http://kwk.us/recoil.html"
Enter the really tricky part... :)

Ron
 
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