Heat of explosion vs. Burn rate

[tbrice23]

Can anyone help me wrap my head as round why H50BMG has a very high heat of explosion but is one of the slowest powders on the chart?
It almost the same HOE as Varget.

And wondering how bad H50BMG is for barrel wear at the same pressure as say RL33, US869 or Retumbo .

Thanks.

 

[Mikecr]

Norma and Vihtavuori powders are like this as well.
RL33 is 3900, IMR 7828 is 3850. Accurate 8700 was among the coolest of all powders at 3460. Truly magic stuff..

Also, we burn barrels out many thousands of shots before wearing barrels out.

 

[tbrice23]

Mike, do you know how HOE is related to burn rate? Or is it?

Hodgdon says H50bmg shares chemistry similar to Varget... so it just has a lot more deterrents??
Maybe?

 

[MagnumManiac]

You do realise that HOE changes due to application?
Just as burn rates are not constant, neither are HOE in different cartridges.
All of this information, burn rate, HOE and KJ numbers are found using a Calorimeter Bomb. This only measure Pressure, Temperature and Gas Volume released in a set volumetric cylinder.
Gun powder behaves differently to this in a cartridge, it even burns differently depending on cartridge size.

I would assume that H50BMG has such a high flame temp due to the size of the kernels and amount used in the test.

Cheers.

 

[Trnelson]

I'm not so sure that there is a direct and simple correlation between heat and burn rate considering smokeless powder. Deterent coatings manipulate the rate of deflagration, but not necessarily the heat of that process.
I would think that there could be a closer relation between heat and energy as in F=M*A and P=F/A As in how a given powder charge can yield a certain velocity at 30• and a higher velocity at 90•
Further, the rate of acceleration (of the bullet) is directly dependent upon the velocity of the expansion of a fixed volume of gas (XX.X grains of a particular powder) acting within a fixed vessel (your barrel) due to deflagration.
You make a good point though as Boyle's Law states that the relationship between pressure and volume is known as Boyle's Law states that: At constant temperature, the volume of a fixed amount of a gas is inversely proportional to its pressure.

 

[BallisticsGuy]

Powder heat is the total energy you can yank from the powder, how many BTU's burning it generates. Burn speed is how long it takes to do that. There's another measurement in gunpowder called bulk density which is how much weight fits in volume X. When taken all together you now have a map of how the powder performs. It's not that they're unrelated but burn speed, bulk density and powder heat are not dependent on each other at all. The resulting pressure over time curve in the barrel is what is dependent on those 3 things. What comes out at the end of the equation is more or less pressure @time, an expansion ratio, a total gas volume and an expansion speed.

 

[ShtrRdy]

Is there any information online which can explain these relationships in such a way that a person might be able to understand?

 

[BallisticsGuy]

Depends on your level of mathematical fluency to be perfectly honest. I can make some analogies that might help clear things up. For some people you point out Boyle's law and they suddenly get it. For others it takes a slightly longer explanation (probably because nobody ever explained Boyle's law to them).

BTU/weight=powder heat = how many pounds burned to get N number of BTU's back.
weight/volume=bulk density = how many cups equal 1 pound.

Those are the easy two. Burn rate is closer to how many logs you need to keep your house warm overnight in the winter.

Bulk density is how much each log of a given physical dimensional size weighs, much like the difference between 1 cubic foot of balsa wood, 1 cubic foot of pine wood and 1 cubic foot of mesquite wood. Balsa is low density with almost no energy and it'd take a truck load to keep the house warm. Pine wood is in the middle and it'll take a good number of cubic feet to warm the house. Mesquite is dense as rock and it'd take astonishingly few cubic feet to keep the house warm.

Burn rate is partly harder to splain' to the uninitiated because it's a referential measure. It's a measurement made as a reference to another measurement. That's like saying "This hay bale is 2.5 alfalfa bales heavy." That's great info as long as you're extremely familiar with the physical weight of an alfalfa bale. So don't think of burn rate as a hard and fast number with a meaning that is useful in the real everyday world. It's not.

Think of burn rate instead as resistance to ignition. If you make something harder to ignite then it takes more energy (called initiation energy) to light it up. Each reaction (combustion event in this case) only produces so much energy. More of that energy soaked up in the work of overcoming resistance to ignition of the fuel that's producing then energy in the first place means less energy that will come out of the total burn as free energy that can be used to do work.

It's actually just like with gasoline grades. 91 octane is harder to light off than 87 octane. With 87 octane you actually get more power from each unit of mass of gas but with 91 octane it takes a little more energy to light it up so you an use more aggressive timing settings which also means more power (power that is unavailable to the 87 octane because excessive timing causes pinging/detonation that destroys engines though the mechanism of excessive pressure). This is the same situation as heavy versus light bullets with fast powders and slow powders. Too much ignition timing advance is like using too a heavy bullet or too fast a powder. Pressure builds uncontrollably because the plug (the bullet or the piston) can't be moved out of the way fast enough and things explode if the burn is too fast or simply break if it doesn't get to the level of bomb. Not enough timing (or bullet weight or burn speed) means you don't get the power you'd expect from the amount of fuel burned. Slowing the burn speed of the powder is analogous to retarding the timing on an engine (setting the spark to go off later rather than sooner) and it has the exact same effect, that of reducing available power just enough to eliminate damage to the mechanism as a result. So too fast of a powder is like too much timing and too slow a powder is like not enough timing and for EXACTLY the same reasons.

 

[MagnumManiac]

Is there any information online which can explain these relationships in such a way that a person might be able to understand?

As BallisticsGuy alludes to, burn rates are NOT exact between brands, and this is why.
IMR use IMR4895 as their baseline powder to measure RQ numbers. RQ is Relative Quickness. IMR4895 is given a RQ number of #100. All their other powder tested are then either given a higher number (slower burn) or a lower (faster burn) number.
ADI/Thales use AR2206H/H4895 as their #100 RQ baseline, similar to IMR in that respect.
Now, other powder manufacturers such as Alliant/Norma/Vhit/Olin have not made this info public as far as I can ascertain, although the info must be there because QL has got all the relevant info programmed in. I have not been able to source this info even by contacting them.

So, due to powder only EVER being designated a RQ number in house, and no set STANDARD is used to base a RQ number on, there is no way to assume that xxx powder IS actually similar to yyy powder according to a burn rate chart.

BURN RATE IS NOT CONSTANT.

Print this statement out and paste it above your loading bench, and read it before you decide to look at a burn rate chart when choosing a powder to use.
I, and others here, have experienced a powder switching burn rates inexplicably. An example in the 338WM was RE19 behaving much slower than RE22 with 225gr bullets. The RE19 was pushing these bullets over 100fps faster with LESS powder. Have seen the same in the 30-06 with the same 2 powders.

Cheers.

 

[ShtrRdy]

Thanks for taking the time to write up this explanation. I need to digest it and see if I can put it together so that it makes sense to me.

 

[therifleman556]

My head hurts...

 

[Doom2]

Burn rate and heat of explosion are really two independent terms. Heat of explosion (or combustion) is simply the energy released by the powder as it burns. Burn rate is a realative term and as noted depends on a number of factors. For smokeless powder geometry of the cartridge is a factor but the most significant is pressure. A line of H 335 placed on a brick and ignited will burn slowly but placed in a confined space the process becomes rapid as the pressure increases. It is this property that results in smokeless powder being defined as a propellant as opposed to an explosive.

As noted burn rates are relative and there is no standardized test procegure that I'm aware of.

 

[tbrice23]

As noted burn rates are relative and there is no standardized test procegure that I'm aware of.

There should be an independent industry standard. Obviously Alliant doesn't have a clue when they labeled Reloder26 instead of Reloder24. And Reloder23 instead of Reloder21.

 

[tbrice23]

Depends on your level of mathematical fluency to be perfectly honest. I can make some analogies that might help clear things up. For some people you point out Boyle's law and they suddenly get it. For others it takes a slightly longer explanation (probably because nobody ever explained Boyle's law to them).

BTU/weight=powder heat = how many pounds burned to get N number of BTU's back.
weight/volume=bulk density = how many cups equal 1 pound.

Those are the easy two. Burn rate is closer to how many logs you need to keep your house warm overnight in the winter.

Bulk density is how much each log of a given physical dimensional size weighs, much like the difference between 1 cubic foot of balsa wood, 1 cubic foot of pine wood and 1 cubic foot of mesquite wood. Balsa is low density with almost no energy and it'd take a truck load to keep the house warm. Pine wood is in the middle and it'll take a good number of cubic feet to warm the house. Mesquite is dense as rock and it'd take astonishingly few cubic feet to keep the house warm.

Burn rate is partly harder to splain' to the uninitiated because it's a referential measure. It's a measurement made as a reference to another measurement. That's like saying "This hay bale is 2.5 alfalfa bales heavy." That's great info as long as you're extremely familiar with the physical weight of an alfalfa bale. So don't think of burn rate as a hard and fast number with a meaning that is useful in the real everyday world. It's not.

Think of burn rate instead as resistance to ignition. If you make something harder to ignite then it takes more energy (called initiation energy) to light it up. Each reaction (combustion event in this case) only produces so much energy. More of that energy soaked up in the work of overcoming resistance to ignition of the fuel that's producing then energy in the first place means less energy that will come out of the total burn as free energy that can be used to do work.

It's actually just like with gasoline grades. 91 octane is harder to light off than 87 octane. With 87 octane you actually get more power from each unit of mass of gas but with 91 octane it takes a little more energy to light it up so you an use more aggressive timing settings which also means more power (power that is unavailable to the 87 octane because excessive timing causes pinging/detonation that destroys engines though the mechanism of excessive pressure). This is the same situation as heavy versus light bullets with fast powders and slow powders. Too much ignition timing advance is like using too a heavy bullet or too fast a powder. Pressure builds uncontrollably because the plug (the bullet or the piston) can't be moved out of the way fast enough and things explode if the burn is too fast or simply break if it doesn't get to the level of bomb. Not enough timing (or bullet weight or burn speed) means you don't get the power you'd expect from the amount of fuel burned. Slowing the burn speed of the powder is analogous to retarding the timing on an engine (setting the spark to go off later rather than sooner) and it has the exact same effect, that of reducing available power just enough to eliminate damage to the mechanism as a result. So too fast of a powder is like too much timing and too slow a powder is like not enough timing and for EXACTLY the same reasons.

So, how is the HOE number useful at all?