What does powder burn rate tell you?
2.7 grains of Bullseye, #14 on the burn rate chart, is a hotter load tha 7 grains of Trail Boss, burn rate #22.
So how does burn rate relate to performance? Wouldn't volume chang be a better indicator of performances. How does burn rate relate to chamber pressure?

Burn rate can change depending on the cartridge and other factors like, as you mentioned, volume change. Burn rate charts are rough guidelines at best.

Burn rate charts are not directly related to Power Factor or load volume. There is a relationship, but it is not direct. Although faster powders usually require less volume to achieve similar results, the resulting pressure spikes may be less than ideal or even dangerous in some loads. The burn rate charts are estimations and offer limited help in selecting substitute powders. That being said, many of us do find the charts helpful.

Make sure the new powder is appropriate for the application. Correct tool for the job kind of thing.
Start low - based upon the manufacturer's specific load recommendations and work your way up, chrono testing and looking for overpressure signs as you go.

Burn rate charts used to be called "Relative Burn Rate Charts". Charts only show how burn rates relate powder to powder. One powder many be listed as faster or slower than another powder but not by how much. Should be used as reference only...

Ballisticians use the term Relative Quickness (RQ) instead of burning rate. This is sort of an explanation. Relative Burning Speed of Smokeless Powders

Burn rates have no relation to charges used. The burn rate chart can be used to determine other similar powders. You still need to find appropriate load data for each powder. Similar powders usually have similar charges but not always.

Great thread and discussion.
The other chart I started paying attention to
is the Heat Index Chart.

When ever I’m researching a powder I
always look at the:
1 Relative Burn Rate Chart,
2 Heat Index Chart,
3 and is the powder a Single Base (nitrocellulose)
low energy or Double Base powder (% nitrocellulose
and % nitroglycerin) high energy.

For example:
IMR 4350 is #130, Heat Index is 3760 kj/kg
and Single Base powder

Vihtavuori N530 #100, Heat Index 4100 kj/kg
and a Double Base powder.

The V.V. powder is high energy and the rifle
barrel will not last as long and probably
good for long range hunting/shooting.

But that’s just me. I hope this is of use to
someone.

The chart is an indicator of how fast a given powder will achieve its peak pressure compared to other powders listed.

It has to do with maximizing how effectively and efficiently the chemical energy (heat content) of a propellant can be converted into the kinetic energy of the projectile. A gun is essentially a heat engine, just as a gasoline car engine is. You can actually calculate the horsepower of your gun and load fairly easily. A typical .22 rifle is about 90 horsepower.

Where an I find a heat index chart?

Exactly. Also, I have never seen a heat index chart, thanks "Noreseman", but the more chemical energy released as heat per grain burned, your point, will (at least in theory) give you an increasingly more efficient/higher potential loading.
And as stated the heat increase has a price on barrel life. I have seen some X-course barrels go south in 3-4 thousand rounds from max charges of double based powders. They would still be OK for 200 yard work but not 300+.

Look up three different charts and you will see

that they list the powders in different burn rates !!

Data from the powder maker, is the best way to find out what
"Their" powder does, when learning about powders.

Even load data manuals have different amounts of pressues and powder
in their starting and full loads.

It does make for good reading with some head scractching.

Look at a powder like 'Trail Boss'. It was specifically designed to be much bulkier than it 'needed' to be in relation to its burn rate and can fill up a cartridge without overpressure.

__________________
"He was kinda funny lookin'"

I believe a pressure curve (pick the standard cartridge) would be a better means of comparing powders, than some "burn rate" chart.

I also believe, the reason industry puts out a burn rate chart, is so we reloaders don't have good data to compare powders.

Here are the Heat Index Charts I’ve
acquired.
I hope they can be seen ok and useful.

Attached Images

IMG_2248.jpeg (164.7 KB, 55 views)

Here’s the other one with Pistol powders.

Attached Images

IMG_2250.jpg (103.3 KB, 69 views)

Might be just me but what does the chart(s) have to do with powder burn rate The Norseman?

Thanks Norseman.
The units, energy/mass, make more sense than mass/time, when comparing powders.

Very interesting charts. I am surprised at some of the numbers. I used a lot of H-322 shooting IHMSA and always considered it a mild powder but that chart listing may explain why my first 7TCU barrel wound up with rings in it. Thanks for the information.

I recall when Bullseye was rated #1 and WW231 #2 on the progressive burn rate chart. I believe pressure/heat has much to do with how propellant acts relative to cartridge/projectile, case volume, shoulder geometry, free bore ...

__________________
"Don't Give Up the Ship"

I remember when w231 was not on the data sheets, yet.

Bullseye, Gray B, PB, 230P, Top Mark, Unique and the new 700x !

My pappy finally gave up the old powder Horn.

Maybe I do not see things as others do. I used the "Burn Rate Charts" to figure out what powders to use in what barrel lengths. In another words I wanted to use Bullseye in a 2 1/2" barreled revolver and 2400 in a 7 1/2" barreled and not the other way around. Quicker burning powders in short barrels and slower burning powders in longers barrels.

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USMC 69-93 Combat Pistol Inst.

This is like attempting to drink from a fire hose, but what is involved in these questions can be found here: https://apps.dtic.mil/sti/tr/pdf/AD0462060.pdf

This should help in finding an efficient load as to charge weight.

I first ran across this 1965 manual on "Interior Ballistics of Guns" while doing graduate work on Thermodynamics of Convection in the Atmosphere, which uses very similar Calculus equations, (Equation of State and derivatives, or rates of change) requiring understanding of Integral and Differential Calculus to follow the expansion and cooling of the atmosphere in vertical motion (thunderstorms) and predict the winds and hail potential from a vertical sounding of the air on a given day.

Without doing the work to learn calculus, the turbulent physics of interior ballistics of guns, or violent thunderstorms in the atmosphere are too complicated to understand, and cannot be expressed in the static world of arithmetic or algebra.

That's why we have tested loading charts, safe to use by people who don't really understand interior ballistics; and weather warnings for public use in avoiding tornadoes, hail, and severe winds, for people that cannot analyze a skew-T balloon sounding.

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Science plus Art

I'mma gonna" park this right here despite my better judgement in the larger scope of things.
This can get the ignorant noob into trouble if this, the subject matter involved and all manor else about reloading is not fully understood.

However, in the context of this thread, this is a cheap quick and dirty means of taking everyone to the virtual zoo to poke the animals without getting bit.
use of this to go to the real zoo to poke the animals is best avoided without solid understanding of how the zoo really works.
start [Gordons Reloading Tool Community]

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it just needs more voltage

Have you chronographed that? I'd be surprised if what you say is true there.

I'd not be ... trail boss and accurate 5744 are specialized propellants for reduced loads. I expect these to act like they are in business for themselves.
These seem to do the job of unique or red dot in things like 45-70 from very old cast lead data, while doing a better job of it.

__________________
it just needs more voltage