Slower Burning Powders ranked numerically by burn rate

[4thefunofit]

You are very correct in some regards......The only way to get a velocity which is a proxy for gas push from the explosion in the chamber is to model the whole system. That means length of your bbl. Your caliber, what weight bullet you are shooting,
and the size of your chamber, freebore, AI , etc. Also, your bullet seating depth and coal.
Those physics are what make an internal balistics model like GRT or Quickload.

But as a starting point ,if all you want to know is for my rifle system, which is a constant , what powder can get me a higher velocity without exceeding safe pressure in a relative sense , which is a slower burning powder with more gradual gas expansion and pressure, then the starting point on the burn rate curve is a good relative comparator. Thats the BA factor.

So BA is actually a measure of how much gas is produced (pressure), and not a measure of how fast a given amount of powder burns (g/sec). It seems obvious that different chemical compositions would vary in both these factors.

 

[Veteran]

So BA is actually a measure of how much gas is produced (pressure), and not a measure of how fast a given amount of powder burns (g/sec). It seems obvious that different chemical compositions how fast a volume of powder burns, but in the physics, it is the starting point for a curve of burn rate.

No, it is a measure of the volume of powder burned over time,
But its directly correlated to how much gas is produced from the explosion over time, the same way pressure is a proxy for velocity.

 

[Veteran]

To get really technical the units of BA are 1/Bar

And its the measure of the burn rate of the outer layer of powder as combustion iniates.

It gets multiplied by the heat of explosion, the specific heat ratio, a degradation factor, and the density of the powder to generate a curve showing in milliseconds how the explosion generates using that powder.

Yes every powder is different in its granularity and density and other chemical properties, so even 2 powders like IMR 8133 and N568 having the identical BA of .3 wont react completely identically, but they will be very very close.

These factors for each powder are derived by exploding equal volumes of powder in a pressure bomb at same temperature. Equal pressure, temp and volume and with sophisticated instruments determing burn rate, how fast the reaction begins, and how fast it ends in milli seconds.

Something like that.

 

[4thefunofit]

No, it is a measure of the volume of powder burned over time,
But its directly correlated to how much gas is produced from the explosion over time, the same way pressure is a proxy for velocity.

Well, if it's volume, then that introduces another variable because similar volumes can have different densities. Sorry, but I suppose I'm just not understanding the method, and I'm stuck on the amount of gas/unit time for the same weights as what makes sense. And, yes, that should change depending upon pressure and temperature, but it's only a relative index.

 

[4thefunofit]

To get really technical the units of BA are 1/Bar

And its the measure of the burn rate of the outer layer of powder as combustion iniates.

It gets multiplied by the heat of explosion, the specific heat ratio, a degradation factor, and the density of the powder to generate a curve showing in milliseconds how the explosion generates using that powder.

Yes every powder is different in its granularity and density and other chemical properties, so even 2 powders like IMR 8133 and N568 having the identical BA of .3 wont react completely identically, but they will be very very close.

These factors for each powder are derived by exploding equal volumes of powder in a pressure bomb at same temperature. Equal pressure, temp and volume and with sophisticated instruments determing burn rate, how fast the reaction begins, and how fast it ends in milli seconds.

Something like that.

Sounds fun! Thanks!

 

[Veteran]

Well, if it's volume, then that introduces another variable because similar volumes can have different densities. Sorry, but I suppose I'm just not understanding the method, and I'm stuck on the amount of gas/unit time for the same weights as what makes sense. And, yes, that should change depending upon pressure and temperature, but it's only a relative index.

Ok, well good luck. youre free to use the charts and ignore my
relative scale.

 

[MagnumManiac]

One problem with all of this is that no company making powder has a standard to base their results off of.
Instead of using calorimeter tests these days, due to cost, most are using pressure predictions, which is incorrect as far as I see.
Having my own pressure trace, I see quite often that due to the absence of using an average instead of actual max pressure, which is what SAAMI does now, the pressures on factory ammo is way lower than what it used to be, and reloading manuals are the same.
I would like to know how you come across this BA number, because if this is a heat number, then it is meaningless.
The other problem is, you don't know the volume of powder tested, so this is also flawed.

Cheers.

 

[Redfoot Ranch]

Staball HD is a new powder.....

You forced me to order the update disk for my program.....

So, I will answer this when I get the update.

Its probably between RL26 and N570 though.....my guess.

I have my doubts if the new StaBall will be on QL update yet. It's fairly well known by guys running 6.5 StaBall that the default Ba is off considerably.

 

[Veteran]

I have my doubts if the new StaBall will be on QL update yet. It's fairly well known by guys running 6.5 StaBall that the default Ba is off considerably.

How much off?

I adjust my BA factors to actual chrono velocities to history match.

From different lots of powder I have seen 5 to say 12% variance in the model default for a number of powders.

Now for Staball 6.5, which Butterbean says is only good for campfire starter or fertilizer
how much variance are you seeing?

 

[Redfoot Ranch]

How much off?

I adjust my BA factors to actual chrono velocities to history match.

From different lots of powder I have seen 5 to say 12% variance in the model default for a number of powders.

Now for Staball 6.5, which Butterbean says is only good for campfire starter or fertilizer
how much variance are you seeing?

6.5 StaBall has default values of .5400 in QL and .5511 in GRT with real world results of .4900 with MV adjustments after measurable inputs and weighting factor have been properly adjusted.

 

[Veteran]

ok, so it can vary 10 to 12 % too.
How much of that do you think is temp. vs. just lot number or
inaccuracy in the lab tests?

 

[VarmintBob]

Just as an informational note, BA or burn rate or whatever you want to call it varies with case size, bullet size, size of the hole in the end of the cartridge as well as humidity when the cartridge was loaded and temperature when the cartridge is shot. And the default values in QL for Staball 6.5 are way wrong.

 

[Veteran]

Just as an informational note, BA or burn rate or whatever you want to call it varies with case size, bullet size, size of the hole in the end of the cartridge as well as humidity when the cartridge was loaded and temperature when the cartridge is shot. And the default values in QL for Staball 6.5 are way wrong.

Id be interested in your experience w Staball 6.5

In my experience the most gross deviation I have seen for BA has been due to temperature.

Normally, I might see 5 or 12% deviation in normal temps or in changing lot numbers of powder from default which is always at 70 deg F.

If you manipulate input temperature, you will see it changes BA.

And in the real world this is exactly what happens. Over 90 Degrees and in a hot chamber that may be 120 or 130, you can throw default BA out the window.

So, what have you seen w Staball 6.5?

Its showing .54 burn rate, just a tad slower than H4895 and faster than H4350.

But it may be very temp sensitive, especially if you are shooting rapid semi auto in an AR platform w hot chamber?

Butterbean says its good for campfire starter and fertilizer.....

 

[rsnell]

I do not use burn rate charts. I use updated manuals to determine the better powders to try.