Powder burn rate questions

[Johnforrest]

Put together a new 357 Sig rifle with 16" barrel. It came with a crazy short gas tube (shorter than pistol) The fella that made it said "get all the gas you can to make her run right". I had been loading with Longshot for my pistol, so I wanted to see if this would work in the new rifle... Nope.

He recommended Power Pistol? So a bit confused, I loaded a few up in the mild range and they worked like a charm.

When I asked him about it. He said according to Quick Loads, long shot burns up 5-6 inches down the barrel while Power pistol is still burning at 16".

Looking at burn rate chart this doesn't make sense to me? What am I missing?

 

[ligonierbill]

Well, that's not what I get from QL, although PP does maintain pressure a bit longer. Burn rate is only one factor. Without delving into all the variables, common wisdom is that PP is "gassy", which is what you want. And apparently what you got. I shoot 357 Sig from a P226 4.4" barrel. I use PP for 147 XTPs, but mostly I shoot 125s over AA#9.

 

[Johnforrest]

Another way to ask my question is "What besides burn rate would effect how much gas is available to cycle the action". Power pistol is faster on the burn rate chart than Longshot?

 

[ligonierbill]

I can only list what QL says, don't ask me to explain:

Heat of Explosion PP 5,150 Longshot 4,000
Rate of Specific Heats PP 1.2070 Longshot 1.2240
Burning Rate Factor PP 2.1300 Longshot 2.500
Pro- or Digressivity Factor PP 0.1500 Longshot 0.6395
Progressive Burning Limit PP 0.250 Longshot 0.249

Note in particular the Heat of Explosion, which is in units of kilojoule/kilogram. Not a ballistician, but PV=nRT. More heat, more gas volume.

 

[Shadow9mm]

Im no scientist, but as i understand it, in general, a larger volume of powder has the potential to create a larger volume of gas. And for the same cartridge, slower burning powders generally requires larger ammounts of powder to achieve the same pressure.

So if you want to create more gas volume to keep pressure up in a longer barrel, you want powders that are on the slower burning side for the cartridge.

On a side note, i have found power pistol to be a very gassy powder and to work very well in longer barrels with small cartridges.

 

[mehavey]

Type	        Wt (gr)   vel (fps)	Pmax (psi)	Burn (%)  Pmuz (psi)
POWER PISTOL	12.4   	     2,013	 55,000	        100	    22,073
Longshot	12.8	     1,924	 55,000	        100         18,641

I set the muzzle at 6" to replicate short gas tube. Pmuz therefore is what that port sees.

Longshot is faster burning to start/far more progressive in pressure rise after start (and burns out faster)/less energetic as it burns.

Look at the difference in port pressures as a result.

 

[Shadow9mm]

I tested several powder for 44spl in a 20in barrel henry with heavy bullets, 240 to 280g. I tested HP-38, Power Pistol, CFE Pistol, and H110. Most powders performed poorly. especially CFE Pistol. Got very strange reading in the 150-450fps range. sounded very odd almost like it was suppressed, but they made it over the chronograph. However I put that same cartridge in my friends GP100 in 44spl, and it went bang and around 750fps every time. Shooting pistol cartridges in rifles can make them do weird things. of all the powders I tested Power Pistol was by far, hands down, the best performer. My friend uses unique with decent results but I did not test it myself

 

[Marco Califo]

Burn rate charts are only useful to identify powders in a suitable range for an intended application. Trying to "read" anything else into or from burn rates is wrong and unsafe. Only use published data for loading data. Leave burn rates away from your reloading bench.
NEVER DRAW A CONCLUSION FROM A BURNRATE CHART. USE RELOADING DATA ONLY

 

[tangolima]

Grain for grain, PP has more energy and it burns slowly and continuously. It maintains high port pressure during the dwell time. All that gives more energy to cycle the action.

Burn rate chart itself is not evil. It is how to use the information that could give you trouble. There are different types of chart. The worse type is the single column that lines up all powders from all manufacturers. Multiple column type is much better. I throw away the first type and only use the second type.

-TL

Sent from my SM-N960U using Tapatalk

 

[Unclenick]

The burn rate, as expressed by the burn rate factor given in QL, is not what is in the charts. Nobody in the business will pay the lab costs associated with finding that information for their competition's powders. Instead, the chart is what is called a relative burn rate chart. To make one, they take one cartridge and one bullet and load the same charge weight of all the powders on the chart into it, and then rank the powders in descending order of the peak pressure produced. They switch cartridges where necessary to avoid blowing things up or failing to get a bullet out of the muzzle. This is supposed to take the effects of all the other powder specifications into account. The problem with it is that if they pick a different set of cartridges and bullet weights and construction, the order of the ranking changes. A light bullet can go down the tube too fast for a slow powder to keep up with expansion, and a heavy bullet increases the time a fast powder has to peak before expansion becomes significant. It's a complex dynamic system, and thus the results are only somewhat useful when you don't know the particular cartridge and bullet the chart user wants to load for.

 

[mehavey]

they take one cartridge and one bullet and load the same charge weight of all the
powders on the chart into it, and then rank the powders in descending order of the
peak pressure produced.

If as you describe, UncleNick, that "relative" place on the various "Burn Rate" charts
has nothing to do with true burn rate -- anywhere in the pressure cycle.

In fact it tends more to produce a dog's breakfast than useful information.

Wow...

,

 

[tangolima]

The burn rate chart is still useful. I know powder x is faster than y. If it is safe to load m grains of powder x, it is probably won't over pressure if I load m grains of y, etc.

I think manufacturers are willing to spend money on analyzing competitor's product, if that's their competition and accurate info is not readily available. Mostly it is available. Bought a license of QL and you have it.

-TL

Sent from my SM-N960U using Tapatalk

 

[Unclenick]

I know powder x is faster than y

But you don't know that from the relative burn rate charts unless you know the chart was developed using your cartridge and bullet weight. Unfortunately, the chart makers don't usually publish that information. In one exception, Norma has a thorough description in their hardbound #13 manual of a relative burn rate chart developed by Eurenco/Bofors using a 146-grain FMJ bullet in a 308 Winchester and tested in a special, very high-pressure test gun. They give not only the order but the actual relative pressures and the velocities measured for each powder tested. They point out that if they had instead developed the load with a 7×64, the order of which powder was relatively faster (made higher peak pressure) than another would change in some instances. It wouldn't change enough to make, say, Bullseye slower than IMR4350, but among powders in a narrower application range, they could shift around. Indeed, it is easy to find burn rate charts with powders in different orders. So, no, you can't rely on a burn rate chart to predict likely pressure outcomes. Also, understand that they buy powders for the tests off the shelf and don't know if they got a lot that was faster or slower than normal.

I think a much more honest way to devise burn rate charts is where they just have horizontal rows of powders for similar applications. Here's an example. They don't say charge weights will match at a given pressure.

 

[Johnforrest]

Mehavey, Thank you for the CL info. I apologize for not responding to this sooner. I also asked about it in another forum and misplaced "the firing line" in my saved places on this question. I hate it when guys use a forum and don't finalize a question.

An aside.. my 1911 likes Power pistol and my glock 24 likes longshot. I'll stick with PP to keep loading simple. Cast bullets and powder coated sure work nice. This 357 Sig AR was a fun project. 16" barrel, gas operated, and Glock magazines.

 

[Unclenick]

...Also note from earlier in the discussion that the energy density (kJ/kg) is greater for PP. This comes from it being a double-base powder with both nitrocellulose and nitroglycerin in it. Nitrocellulose has a negative oxygen balance when it burns. That is, the amount of carbon, hydrogen, and nitrogen released from it that could be oxidized is about 24% greater for cellulose hexanitrate (the main nitration of the cellulose) than the amount of oxygen released can oxidize. This is why there is carbon left in the bore. Nitroglycerin, on the other hand, has about a 3½% oxygen surplus when it burns. Thus, not only does it oxidize completely, it provides a little extra oxygen that reduces the nitrocellulose oxygen deficit a little. The net result is more oxidized gas molecules (CO, CO₂, H₂O, NO, NO₂, HNO) are produced per grain of the double-base powder than you get with a single-base powder.

I think manufacturers are willing to spend money on analyzing competitor's product, if that's their competition and accurate info is not readily available. Mostly it is available. Bought a license of QL and you have it.

I'm sorry I missed this post when the thread was still new. Actually, I got it directly from Hodgdon a while back that they do not test competitor's products. I was looking for data on a powder not listed in QL at the time (Hodgdon and others) and asked if they had it. I was told it costs something like 30-50 k$ to have a lab fully characterize a powder, so they would have to spend millions to get all their competitor's powders analyzed. And then, what would they do with the information? They order powder made to a formulation rather than to all those modeling characteristics, which would be hard to control independently. A finished lot of powder then has only its burn rate tested. The new lot is then milled (blended) with held-back past lots of the same powder formulation that came out of the factory either faster or slower, whichever is needed, to bring the relative burn rate of the new lot in line with their reference powder's performance, plus of minus 3%. I assume this test is for relative burn rate rather than the PET-initiated water tank test of burn rate that determines Ba. The relative burn rate test is simple and more meaningful when you are comparing it to past lots of the same formulation rather than comparing different formulations whose different characteristic burning curves will affect outcomes. This relative burn rate test just involves loading the same charge into the same cartridge component combination and blending to match the peak pressure results with what the reference lot produces. Not too complicated.

For the modeling numbers, QL's author, Hartmut Broemel, uses a clever workaround. He owns the lab equipment to do his own vivacity bomb test, then uses the output of that single test to deduce the other powder characteristics. This deduction function is built into the program, just in case you are able to get your own vivacity bomb testing done. You click on the powder editing button. In the lower-left corner of the window, click on the bottom button to choose to edit bomb output, and you get a table that lets you put in the vivacity bomb time and pressure numbers. The software then generates the full list of characteristics from that information. So, the powder characteristic tables in the program are not lab-determined independently tested characteristics but rather are "behaves-as-if" numbers deduced from that one test. This is kind of the heart of Herr Broemel's invention of the software, this clever lab shortcut. How exactly it compares to independently determined characteristics depends on several things, but it gets reasonably close. You can tell because some of the powder makers on the other side of the pond publish some of the characteristics they've measured for their own production (these are actual powder makers, not distributors like Hodgdon). Vihtavuori and Somchem, for example, will give you some numbers, like energy content, and you can compare them to what's listed in QL. They don't match exactly because the factory publishes target numbers, and Herr Broemel's measurements are of lots purchased off the shelf and tested. He has no way of knowing exactly how close to average a particular test lot is, so his numbers will shift some from the makers' target numbers because their lots shift some from their target values.

If you read the QL manual completely, a lot of that information is in it.

 

[243winxb]

Very OLD. Post

Port pressure works AR15 actions. Try an adjustable gas block? The port diameter may be the wrong size. There are many diameters in use.

 

[RC20]

In a nutshell, if I see a new powder and want to know what its general relevance to a caliber is, I look at the burn rate chart. Its a ballpark and nothing else.

Worst case you can get its relevance with other burn rates just above or below and see what the loads are and do a minimum load (better if you have a chrono graph)

But for specific application you have to test and gas operated guns are world unto themselves and then research into who uses what for as close an application as you can get.

Worst case you do one and see if it cycles the action. Then decide if a higher velocity might do better. Custom guns are a world unto themselves let alone the various gas aspects (be it DI/Gas Tappet or long stroke gas piston)

 

[stagpanther]

I think a much more honest way to devise burn rate charts is where they just have horizontal rows of powders for similar applications.

I call these equivalence charts--is there a difference in the methodology used to determine these compared to faster/slower charts?

 

[tangolima]

I call these equivalence charts--is there a difference in the methodology used to determine these compared to faster/slower charts?

I call that multiple column chart. There are rather rare. It is the type I trust the most. The common single column type is for entertainment only.

-TL

Sent from my SM-N960U using Tapatalk

 

[Unclenick]

Stagpanther,

Good question. I don't have any first-hand information about it. I think you can expect the powder manufacturers to have done the actual testing, especially if they are set up to do it anyway for control of their canister-grade powder burn rates. Big powder distributors like Hodgdon and Alliant likely get the information from their powder suppliers, but they also have universal receivers and could do it themselves if they choose to or if there are gaps they need to fill in their supplier data. But I also see a number of charts of both types published by small bullet makers and online sources that would not be likely to have done the raw data gathering themselves. From the nature of the data, I expect these to be compiled by looking at load manuals and existing relative burn rate charts to see what powders are predominant in different categories for different purposes.

There is a brief article on the Ballistics Assistant site about how to use burn rate charts. They also have a compiled burn rate chart.