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Discussion Starter #1
I have a .460 Rowland in both 1911 pistol form with compensator and a .460 carbine with a 15 inch barrel. I only shoot reloads using either Longshot or Accurate #7 always with Nosler 230 grain hollow point bullets and CCI pistol primers. The pistol produces velocities right at 1300 fps. The carbine produces velocities of 1500 fps. When I look at burning rates of the two powders, #7 is rated faster than Longshot. But when I look up loading data, more #7 by weight is recommended than Longshot. I have also experienced higher pressures with Longshot at the same loading weight. In the carbine I can only use 12.6 grains of Longshot but use 14.6 grains of #7. That is significant. Velocities are about the same with either but #7 gives my carbine better groups so that is what I use. Can anyone explain this? Are burning rate charts in error?
 

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The Shadow (Super Mod)
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Burning rate charts are always approximations, nothing more.

Fixed volume bomb calorimeters don't account for shifting burning rates by volume, or even lot variances(assuming the same producers). When you get into moving blends, and moving suppliers; things can be very interesting.

This is one of the reasons I've cautioned to not put complete faith in calculators such as QL.

Cheers
 
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Burn rate charts are made by using an enclosed powder charge (a "closed bomb"). In a real gun the chamber size grows as the bullet leaves the case. Smokeless powder burn rates increase with pressure and heat. In your gun, with your cartridge, the powder burn rate will change with bullet weight, pull resistance, barrel finish, and jump to the lands.

The charts are built on unrealistic data for use in guns. You will find many examples of powders changing characteristics in load data.
 

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Discussion Starter #4
One thing I failed to mention is that there is a considerable difference in densities. Longshot is 12.1 gm/cc while #7 is 15.3 gm/cc. Therefore an equal charge by weight means there is less vacant space in cartridge using Longshot. That affects pressures.
 

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Also, burn rate charts are not linear either. Powder X can be listed as faster than powder Y, but how much? Increase of 5,000 psi, or 25,000 psi (how measured? psi per second?). And is powder Z the same difference than powder Y? That's why they are called "Relative Burn Rate Charts"
 

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Elk Whisperer (Super Moderator)
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Here's just one example of twins in different dresses:



Both can be loaded almost identicslly, but due to different lot numbers from the "source" their "burn rate" is different. I now have, in affect, several pounds of either IMR4064 or Reloader 15 with so far the only cartridge they work well in is the .308 and my .308 hasn't been shot in years although I do load for a couple others.

Woe is me.

Not being one to be taken in by all the new wonderful powders that are supposed to produce magical velocities and teeny groups I have recently fallen prey to the songs of "Hybrid 100V" and "Superformance" I bought and was disappointed by both along with 7828SSC, Retumbo, H50BMG, Rx25, 23 and 22, US879 and many many others so that my powder magazine looks like a varitable "who's who" from every US powder supplier. I will not ever succumb to the siren songs of any of the CFE line of magical fairy dust.

So, now when people ask me "Hey! RJ, have you tried GGGGCCCKK!" I immediately grab their larynx and reply in my best Liam Neason " Bugger off mate. Keep pestering me and where ever you go I will track you down, I will find you and I will kill you."

Anyways, that's my take on burn rates.

RJ
 

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The Shadow (Super Mod)
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...I will not ever succumb to the siren songs of any of the magical ...
Awfully serious sounding, RJ..
Sounds a little more like you answered the idiots bugle, not the sirens song.:LOL::LOL::LOL::ROFLMAO::ROFLMAO:


Cheers
 

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Elk Whisperer (Super Moderator)
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Awfully serious sounding, RJ..
Sounds a little more like you answered the idiots bugle, not the sirens song.:LOL::LOL::LOL::ROFLMAO::ROFLMAO:


Cheers
That sounds like a challange, or duel if you will. Your bestest CFE load against my Benchmark load out of my four .223's, you pick.

Loser buys dinner curbside at Gino's Pizzeria and Burger Barn, adult beverages on my deck after.

RJ

😜😝😵
 
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“Well, here's another nice mess you've gotten me into!”
Oliver Hardy


The first thing to realize is a powder’s characteristic burn rate factor, Ba, which has units of 1/bar-seconds* is not what you find ranked on the relative burn rate charts in load manuals or from suppliers. A minor reason is U.S. suppliers don’t publish that number for their powders, and nobody wants to spend thousands of dollars on vivacity bomb testing of their competitor’s products. The main reason is that while the burn rate factor is part of what influences a powder’s behavior, it isn’t the only factor you need to predict its expression in a specific cartridge. So, in isolation, it isn’t a number that is directly useful to the handloader.

For example, suppose two powders have the same burn rate factor, but one has more stored chemical potential energy than the other, as can happen when you compare same-burn-rate single and double-base powders. If you load the same charge weight of both powders for the same gun using the same other components, the higher energy powder will produce higher pressure. Higher pressure will make it burn faster, so its apparent burn rate will be faster in your gun and cartridge than the other powder’s will, even though Ba is the same in both. You will need less of the higher energy powder to reach the same peak pressure, and, because it produces more gas per gram, even less than that to match velocity. The extra gas delivers more bullet acceleration in its travel beyond the pressure peak.

A third reason comparing Ba numbers doesn’t help a great deal is the closed vivacity bomb test sees pressure rise until the powder finishes burning. In a gun, the pressure only rises until the bullet is moving fast enough that the rate of expansion of space behind the bullet equals the rate at which the powder is evolving additional gas. In a rifle, that usually occurs when the bullet is an inch or so past the throat. Beyond that position, the bullet keeps accelerating, and expansion becomes faster than the powder can make gas, resulting in pressure dropping and the remaining powder burning more slowly until the bullet clears the muzzle. That is true, regardless of whether the powder has all burned up by then or not. It is also the reason you use either less powder or a slower burning powder with heavier bullets. Heavier bullets don’t accelerate as quickly as light bullets do with a given pressure. That means the pressure is going to peak in a smaller, less expanded volume when you use the same powder, or you can use a slower powder to reach the same peak pressure after giving the bullet more time to expand the burning space. This is also why using an effectively faster powder costs you velocity, while an effectively slower one does not do so in the same situation.**. The bottom line is, constraints that exist in the bomb and those in a gun don’t match.

To address the above limitations with relying on Ba, and to better reflect powder behavior guns, the unitless relative burn rate concept was developed. The method of gathering data is to put the same charge weight of every powder being ranked in the same cartridge with the same bullet and case and primer. These are fired in a very, very robust pressure gun, and the peak pressures are recorded. The powders are then ranked in descending order of the peak pressures they produce.

From Norma’s 2013 manual, page 89:

“When comparing different burning rate charts, one will notice variations in listed propellant ordering. Still, each chart tells the “truth”. Ranking differences result from use of different criteria. For example, a certain powder type can act slightly quicker than some other powder type, when used In 308 Winchester loads; however, when these powders are used in 7×64 Loads, evident burning rates might reverse. Relative burning rate charts can never provide absolute data because too many factors are involved in how propellants burn within a cartridge chamber.“​

They go on to describe a chart Eurenco/Bofors created using the .308 Winchester cartridge with a 143-grain FMJ bullet. They put 42.3 grains of each powder in the test gun and fired them. They used IMR 4350 as the reference powder for which pressure and velocity were both called 100%. The powder relative burn rates are then ranked from fast to slow in descending order of the peak pressures given as multiples of the 4350 peak pressure. This form of data collection automatically compensates for energy level differences, burning curve shape differences, and other factors affecting the “apparent” burn rate of a powder used in this load and at the pressures actually observed.

A problem with relying on relative burn rate charts is illustrated in the 1995 Precision Shooting Reloading Guide. Dave Milosovich fired 180-grain bullets using both IMR 4895 and 4064 in a .308 Winchester rifle, loading them to achieve specific average muzzle velocities rather than pressures. He found it required a smaller charge of 4064 than of 4895 to achieve 2200 fps, indicating 4064 was the faster of the two in practical terms. He found the two powders needed identical charge weights (within 0.1 grains) to achieve 2400 fps, suggesting the burn rates were essentially the same in that load. He found it took more 4064 than 4895 to achieve 2500 fps and above, suggesting 4064 was the slower powder at the pressures need to get to those velocities. So 4064 seemed to rank as faster burning at pressures that produced velocities below about 2400 fps, and it ranked slower at pressures that produced velocities above 2400. What is the correct relative burn rate order for these two powders? It depends on the pressure you are loading to and the expansion rate you achieve.

The mechanism in the above experiment was that 4064’s apparent burn rate is less affected by the rising pressure associated with the higher velocities than 4895 was. You can see this for yourself in Hodgdon’s data. For any powder in a load you are interested in, take the difference in the maximum and starting pressure and divide it by the difference in the maximum and starting charge weight. The result will be in fps/grain. You will usually find it is a little smaller for 4064 than for 4895 and occasionally a lot smaller. Varget is often smaller still. But the differences you see with different bullet weights or even with entirely different cartridges will give you some sense of how much the apparent burn rate actually moves around.

*The inverse (divided into one) of the impulse created by pressure developed in a closed vivacity bomb multiplied by the time that pressure took to develop. As the time required increases due to slower burning, the inverse gets smaller, lowering Ba.
**By this I mean a powder that actually behaves as a slower powder in your load, and not just that it claims to be slower on a relative burn rate chart.
 
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An important comparison between powders/loads is pressure variation.

From loading tables note that powders/loads have different maximum pressures than others. Testing determines the pressure swings which must be statistically accounted for so that a safe pressure is never exceeded. Loads are backed down to ensure compliance with safety margins. If there were no variation, loads could go to the maximum safe operating pressure.

Powders whose max loads approach the highest pressure have the least statistical variation and have the potential to be the most accurate if matched to your rifle's characteristics.

The starting load standard deviation for pressure for different powders tends to improve and converge which is why starting loads are generally more accurate and are recommended as a place to begin load development.

All things being equal as established in a ballistics lab, pressure variation determines the velocity variation for each load.
 

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The way load manuals use the SAAMI standard is different from the way they were designed to be used by commercial ammunition manufacturers. Specific variation is allowed by SAAMI. It is called the Maximum Extreme Variation (MEV). It is is the Maximum Average Pressure (MAP; what we normally think of as the SAAMI pressure limit) times 5.16 times the coefficient of variation (CV) for the cartridge type (4% for CF Rifle and RF, 5% for handgun cartridges, and 7.5% for shotgun shells). The SAAMI standard deviation limit for a cartridge is just the cartridge MAP value times that CV expressed as a decimal rather than a percentage (0.04, 0.05, or 0.075). The result is the spread that 99% of rounds from a load with that SAAMI standard deviation should fall into when loaded all the way to an average pressure that matches the MAP value.

In theory, if a round produced 9 shots that were all -2% below the SAAMI MAP, and the tenth round was +18% above the MAP, the load would still comply with the SAAMI standard (though that is an unlikely event). By comparison, the CIP limits individual rounds in the average to MAP+15%. There is also a SAAMI number called the Maximum Probable Lot Mean that is two standard errors (the standard deviation divided by the square root of the sample size) above the MAP to allow that a subsequently tested additional sample of 10 rounds won't likely match the average peak pressure of the first 10 exactly. This allowance adds just over another 2.5% to CF rifle and RF, 3.2% to handgun ammunition, and 4.7% to shotgun shell pressure limits. And we haven't yet touched on the Maximum Probable Sample Mean (MPSM), which allows even more pressure as the lot ages.

That the SAAMI standard lets the pressure of individual rounds to go over 20% above MAP may shock some folks, but you have to remember the proof pressures are even higher. Also, for example, remember that jamming a bullet into the lands of a rifle cartridge causes about a 20% peak pressure increase, and you certainly want your gun and case to survive that if it happens accidentally.

The reason the above can work is ammunition manufacturers following the SAAMI standard perform pressure tests for every lot of powder they employ in a load. But load manual authors cannot expect handloaders to do that. They have to list canister powder "recipes" for handloaders. These powders can have a burn rate variation of several percentage points from lot to lot. Additionally, not every powder they list is optimal for the cartridge because they know people often want to use something they have on hand. So they want to allow for more burn rate variation than SAAMI prescribes for a manufacturer, not to mention some margin for loading errors. So they do as Swarfer described and use the MAP as an absolute pressure limit rather than a limit for the pressure average. This adds a significant margin of safety and also liability protection for them.

This example is for .45 Auto:

99394
 

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…But with the added limitation to what Mikld mentioned that they are relative as ranked in a particular cartridge with a particular bullet, which often is not the same order they would have using another cartridge and bullet.

On the plus side, it's not like you are going to see Bullseye and H50BMG change order on any chart because they won't change the order in any test cartridge and component combination. So the limitation of the charts is the resolution they have for any randomly selected cartridge and bullet combination. It's coarse, which is why you see powders in a similar range flip order among different charts: the chart developers have chosen different cartridges and bullets. Also, you can't really load the same amount of Bullseye and H50BMG in any cartridge without either bursting even a super-heavyweight action in the one extreme or producing so little pressure the bullet sticks in the barrel in the other. There is no overlapping practical charge weight you can test for those powders among others. This means the chart makers have to transition to different cartridges at some points in the table development. We don't know at which powders that happens on different charts, much less what the different cartridges were.

Another kind of burn rate chart you see does not list powders in an individually ranked order but rather groups them by approximate similarity in pressure-producing speed. This is an example. It isn't collected any differently than the charts with individual listings, AFAIK, but the concept of approximate similarity is more realistic for making powder suggestions. Also, it addresses the issue Mikld brought up as to how much difference there is in the chart description at the top:

"The chart of relative quickness of powders below is intended as a guideline only. Powders within three lines of one another are similar in relative quickness but cannot be directly substituted without due regard for safe reloading procedures.

GSC "​

This gives you a hint as to how you might collect your own chart of that style. Just look at different relative burn rate charts to see which powders change order and put them all in the same group.
 
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