Burn Rate Factor (Ba) - not burn rate chart

[WoodrowShootist]

anyone know where I can find a list of this calculation? Been searching around and seems like I have to contact manufacturers but though I'd try seeing what you guys think. Thanks!

not looking for relative burn rates (burn rate chart) but the Ba or the burn rate factor which is absolute.

[Bill Steele]

If you mean a burn rate chart, see below. If you mean a way to calulate a given powder's burn rate, I have no idea.

http://www.hodgdon.com/burn-rate.html

[blockfort]

That is cool.

[rsrocket1]

Do a Goolgle search on "burn rate factor Ba" and look at the shootersforum "Burn rates gone awry" link. Unclenick has a very good explanation on the uselessness of the popular "Burn Rate Charts" when it comes to real powder performance and how even the powder manufacturers cannot get an absolute match when blending powders, only to within about 10%.

That's why you should always start low and work up when using a new powder, even a new lot # of the same powder you've been using for decades.

[ar15barrels]

anyone know where I can find a list of this calculation? Been searching around and seems like I have to contact manufacturers but though I'd try seeing what you guys think. Thanks!

not looking for relative burn rates (burn rate chart) but the Ba or the burn rate factor which is absolute.

Ba is determined via actual lab testing.
They put a fixed amount of powder into a known volume test chamber and ignite it.
Based on the pressure that it creates, they determine the burn rate.
I don't know the volumes or the scale factor of how the actual Ba number is derived.

Fun reading here:

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA111286

[WoodrowShootist]

Yes exactly and I want to know this Ba value.

[ar15barrels]

Yes exactly and I want to know this Ba value.

Quickload lists it for each powder.

[WoodrowShootist]

it does, but it's not always correct. i wrote to a couple powder companies about specific powders and lots but haven't heard back yet. a buddy did the same and got a reply about a couple powders and the numbers didn't match up.

it seems like it should be a value that changes with lots. but i just want to cross reference. i haven't had the time to observe how it changes but from what my understanding of it is that the Ba value should change based on the chamber pressures that quickload calculates. There's a baseline Ba value and like it's said before that'd determined by burn duration of x amount of powder at a given pressure.

so as your loads change in pressure the Ba should. if you observe this let me know as I haven't had time to play with it lately.

[ar15barrels]

it does, but it's not always correct. i wrote to a couple powder companies about specific powders and lots but haven't heard back yet. a buddy did the same and got a reply about a couple powders and the numbers didn't match up.

it seems like it should be a value that changes with lots. but i just want to cross reference. i haven't had the time to observe how it changes but from what my understanding of it is that the Ba value should change based on the chamber pressures that quickload calculates. There's a baseline Ba value and like it's said before that'd determined by burn duration of x amount of powder at a given pressure.

so as your loads change in pressure the Ba should. if you observe this let me know as I haven't had time to play with it lately.

You can tweak the ba to get more accurate results from quick load.
You can also just tweak the case volume until the velocity lines up.
Adjusting either one is going to get you correct pressures and velocities from your model within the limitations of what you should be trusting quick load to do for you.

[WoodrowShootist]

Yes you can tweak Ba all you want but if its not true to what the actual value is then its just a fantasy load.

I guess I, just hung up on this because by default it can be a totally arbitrary number in quick load and like you said we trust it. But it's documented somewhere and I want to know. Maybe it's not worth chasing haaha.

[ar15barrels]

Think of it this way...
If using the standard ba that quick load gives you and tweaking the case capacity works across multiple powders, just go with it.
Otherwise, measure your case capacity of a fired case, use that, and adjust the ba of every powder to match your actual measured velocity.
Beware that ba changes with case capacity so you won't be using the same ba with a powder in the 30gr charge range than you will in the 50gr charge range...

You are thinking about it too much.

[rsrocket1]

You can't just depend on Ba. If you look at the other parameters, especially the Pro- or Degressivity Factor, it makes an enormous difference in the "speed" of the powder. From personal experience, for instance, Bullseye is touted as being one of the "fastest" powders around. If you simply depended on Ba, then yes it looks very fast but a0 is -0.45. Red Dot has an almost equal Ba, but an a0 of +6.7. That makes the powder much "faster" than Bullseye while the negative a0 puts Bullseye closer to Unique in real cartridge performance.

Load data and personal experience proves this out. When Bullseye is loaded to pressures equal to Unique, it produces near equivalent velocities. Red Dot however, behaves like a much "faster" powder and reaches an equivalent peak pressure way before reaching equivalent muzzle velocities.

Ba can be tweaked for your powder data based on your own chrony data and it's probably the best parameter to personalize when doing apples to apples comparisons for predictions, but the absolute numbers shouldn't be the only thing to consider when trying to predict what powder would be a good choice for a certain purpose.

That's where the Propellant Table Setup Form is really helpful in QL. You can base your "what if" on pressure, MV, fill volume, etc. and choose the range of powders based on Ba and QL will do test runs on each powder and sort their performance based on the parameter you want AND it takes all the other factors including a0 into account.

[Clarkm]

Do a Goolgle search on "burn rate factor Ba" and look at the shootersforum "Burn rates gone awry" link. Unclenick has a very good explanation on the uselessness of the popular "Burn Rate Charts" when it comes to real powder performance and how even the powder manufacturers cannot get an absolute match when blending powders, only to within about 10%.

That's why you should always start low and work up when using a new powder, even a new lot # of the same powder you've been using for decades.

A Google search hits on this thread.

I am glad it did.