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 Post subject: Burn rates
PostPosted: Sun Jan 10, 2021 10:39 am 
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Can someone explain to me how "burn rates" matter to reloading. I load 12ga with a several powders and 28ga with Longshot.I have Clays, International Clays, 700x,and Titewad and load 3/4 oz to 1 1/8, all target loads. What is important about burn rates?
Just trying to learn something.




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 Post subject: Re: Burn rates
PostPosted: Sun Jan 10, 2021 11:10 am 
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The short answer is it determines what shot load it is good for.

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 Post subject: Re: Burn rates
PostPosted: Sun Jan 10, 2021 11:35 am 
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https://www.shotgunworld.com/bbs/viewto ... 3&t=189696


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 Post subject: Re: Burn rates
PostPosted: Sun Jan 10, 2021 12:09 pm 
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That ^^^^ is an EXCELLENT explanation. Burn rate is very important to helping you select a powder that minimizes frustration in trying to build a workable load.

good luck, garrisonjoe


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 Post subject: Re: Burn rates
PostPosted: Sun Jan 10, 2021 2:34 pm 
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With shotshells, IF you are developing loads and are working with powders that you don't have experience with, burn rates are nice to know.

Burn rates as far as the reloader is concerned are fairly useless as the published data tells you what powder to use.

I have always looked at burn rate charts the same way I look at understanding dram equivalent, fun stuff to know but it really doesn't get you anywhere. Why? Because burn rate charts are misleading. Just because powder 'A' is listed before powder 'B' doesn't mean that is what happens when you actually put a load together.

Don't believe me? Look at where Bullseye is listed on a burn rate chart. It isn't even close to where it's useful application with shotshells lie.

Burn rates are developed using what is called a 'closed bomb test'. A shotshell is hardly in that same environment. The information gleaned from those tests is important to someone, but probably no one here. I think an engineer thought it would be a good idea to impress everyone, so he printed up a burn rate chart.

Like I said 'fun stuff to know' but that and a $1.00 gets you a coffee at McDonalds.

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 Post subject: Re: Burn rates
PostPosted: Sun Jan 10, 2021 3:20 pm 
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The intricacies of internal ballistics is beyond my pay grade but the basic explanation as I understand it, is that it is one of the primary variables that defines the pressure curve. How fast energy is consumed & such things as, is the rate linear or variable, determine the before mentioned pressure curve.


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 Post subject: Re: Burn rates
PostPosted: Mon Jan 11, 2021 12:02 am 
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As applied to 12 ga., the lighter the shot charge, the faster the powder needs to be in order to keep the pressure up. Higher pressures make for more consistent performance and clean burn. When you get to 1 1/8 oz, below 1200 fps, the faster powders are OK because the pressures will be below the SAAMI MAP. For most all of the faster powders, the pressures get too high above 1200 fps. Above 1200 fps, you will need to go to a slower powder. And slower powders are inappropriate for shot charge weights below 1 oz.

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 Post subject: Re: Burn rates
PostPosted: Mon Jan 11, 2021 9:20 am 
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Think about burn rates like liquid fuels. Gasoline burns faster than Diesel. Piston engine needs needs appropriate fuel, higher compression slower fuel needed.

Shotgun shell the same.

Bass


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 Post subject: Burn rates
PostPosted: Mon Jan 11, 2021 9:31 am 
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Burn rate is just a relative measurement on how fast the powder burns. Smokeless powder does not explode, but instead burns. Fast powders burn quickly, slow ones less quickly.

Why it matters, think of how we get things moving. If it’s light, like say a empty soda can, a quick tap sends it flying. If it’s full, it takes a longer push to get it moving, with a quick tap doing nothing. Powder is sort of like that. Fast powders for light projectile and short barrels. Need to get the powder burned before the bullet leaves the barrel. With a heavy projectile and long barrel you want slower powders to get the projectile moving and then accelerate it without spiking pressure. If it’s too slow then the projectile leaves the barrel before the powder is all burned.


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 Post subject: Re: Burn rates
PostPosted: Mon Jan 11, 2021 11:14 am 
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Other than understanding a burn rate chart, as in Red Dot is faster than Green Dot because it is listed before Green Dot on a burn rate chart.........

If anyone that has responded to this thread, including me, was given the actual burn rate of a powder, we wouldn't have a clue on how to apply it. I doubt any of us truly understand what a closed bomb test is or how it is conducted and what information is taken from the test and how it is applied.

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 Post subject: Re: Burn rates
PostPosted: Mon Jan 11, 2021 11:41 am 
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Dogchaser, I love your graphics! There are at least two ways to approach a problem. A scientist is interested in knowledge for the sake knowledge. Engineers have to design stuff that works. Sure, they like to know "why" because that helps with the "what works" part but mostly the focus is on what works with the highest degree of reliability. "One good test is worth a thousand expert opinions."


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 Post subject: Re: Burn rates
PostPosted: Mon Jan 11, 2021 11:57 am 
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I agree that we all should be loading shotshells to tested load data, rather than to rough comparisons as provided by burn rate. Burn rate charts are just relative, qualitative and informational. They are a lot more useful to ballistics techs trying to invent new powders or loads, than they are to us loading practitioners.

(FYI - I did perform some closed bomb thermodynamic labs while taking Thermodynamics class a few decades ago. Part of my engineering training.)

good luck, garrisonjoe


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 Post subject: Re: Burn rates
PostPosted: Mon Jan 11, 2021 12:51 pm 
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wrfish wrote:
Can someone explain to me how "burn rates" matter to reloading. I load 12ga with a several powders and 28ga with Longshot.I have Clays, International Clays, 700x,and Titewad and load 3/4 oz to 1 1/8, all target loads. What is important about burn rates?
Just trying to learn something.

Pressure Management, AND Gas Bubble Volume for Velocity Management.

A couple simplified basics to set the stage.
Gunpowder is ALL BURNED LONG BEFORE any projectile ever gets anywhere close to the gun muzzle. Some burn all up before the shell ever even gets to open, others may still be burning with the wad 1/2 out of the hull (but not for much longer).

Muzzle Flash is from superheated gasses (4,000*F or so) reaching open air.

Within certain limits, depending on the exact formulation, gunpowder all produces the same volume of gas per grain of weight/mass.
10gr of powder A makes the same gas volume as 10gr of powder b, and half as much as 20gr of powder C.
Boyles Gas Law states (among other things) that any gas pressure inside a fixed volume, if you double the size of that fixed volume, the pressure will drop by 1/2.
Thus, every time that a bullet base (straight-wall cartridge) or wad gas seal doubles the distance from it to the inside base of a cartridge, pressure drops by half.
This is why, there is NEVER "11,000psi" in a shotgun barrel past the first inch or 2 maybe, no matter what the load is or how short the barrel is.
Same thing for all guns. There is a heck of a lot more pressure at the muzzle of my BAR when it launches a .308" bullet than there is of my heaviest 12-gauge hunting load, but it ISN'T 62,000psi, it isn't even 10,000psi, even though I've burned 48gr of much slower powder to get there.

Pressure Management.
Same load, same velocity, a fast powder will make higher pressure, faster, with a smaller gas volume (because less powder is burned) than the same amount of slower powder, because the pressures involved will start pushing the cartridge apart while the powder is still burning, increasing the volume the gas is burned in, reducing pressure.
This is why you can get a 1-ounce load, 1,200fps at 11,000psi, from 15grains of Fast Powder A while 20gr of Slower Powder B gives you that same 1,200fps at only 8,000psi.

Say you need 1,300fps, Fast Powder A won't do it without exceeding pressure limit standards, Slower Powder B will possibly get you there within pressure standards, if it ALSO comes up short (1,275fps), then Even Slower Powder C would be your ticket to 1,300fps @ 11,000psi.


Velocity Management by Gas Volume.
AS I said, more powder burned, more gas created, the rub is HOW FAST the gas is created.
If the gas creation is nearly instant (1-2 miliseconds) projectile inertia says "nothing moves" and all that pressure is created in a sealed enclosure until that inertia is overcome.
If gas creation is slower, then while powder is still burning, the projectile inertia is overcome, projectile starts accelerating, gas pressure falls EXCEPT pressure is still being back-filled by still-burning gas, so pressure is maintained, not lost.
Once the powder burns out, the volume it was burned in is bigger, and Boyles Law takes over, BUT, the "start point" for pressure loss is larger, so pressure drop is slower, so hard acceleration is maintained longer, so end velocity at launch is higher.

This is how you get a 1-ounce load of shot to 1,200fps with 11,000psi and a very fast burning powder AND you get that same 1-ounce load of the same shot to 1,500fps at the same 11,000psi using a larger pile of slow-burning powder.


Now, everything has a "balance point" where it is really really useful, marginally useful, or not useful.

For instance, Red Dot, a very fast powder, is very good for making medium-weight target loads in 10 and 12 gauge, 7/8 ounce, 1-ounce, 1-1/8th ounce, and thereabounts, 1,200fps plus or minus, at 11,000psi, plus or minus, reliable and clean burning.

Get under 7/8 ounce and the pile of Red Dot required to GET acceptable pressures get BIG (low inertia, shot charge moves easily), AND velocity gets very high from the large gas bubble, so a faster powder is better suited to that.
On the other hand, you COULD actually burn Red Dot under my 1-3/8 ounce Pheasant Grenade, BUT, to not exceed pressure limits (the weight is just too heavy, inertia too high) the amount you would use would be TINY, the gas bubble would be correspondingly small, and velocity would be uselessly slow.
Thus, that Pheasant Load uses, literally, 2.5X as much very slow Blue Dot, at the same pressure level, as my 1-1/8th ounce target load uses of Red Dot, AND it launches at a higher velocity, 1325fps.


As shotgun shell bores get smaller, the effect of boyles law is slower, because the bore diameter is smaller (it is functioning on a smaller scale), so the smaller the bore of a shotgun, the slower the powders that work well in it.
Small Bore shotguns are unable to manage the pressure spikes of very fast powders, so, within pressure limits, velocities would be very poor. Large bore shotguns are unable to burn very slow powders fast enough to obtain useful pressures without using very heavy shot loads on top of them.

This is why you see, when you look at data, that the fast powders like Red Dot disappear at about 20-gauge, sliding in to the "medium-fast-to-medium" powders with the slow powders useful for "magnum" heavy payloads.

The "medium-fast" like Green Dot go away by the 28 gauge, and you have the Medium-and-slow powders. Unique, Herco, and so on.

And the little .410-bore needs VERY slow powders, typically used either for magnum shotgun shell or (even slower) magnum pistol powders.


Was that enough mud for the water??? :mrgreen: :mrgreen: :mrgreen:
I do hope not....

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 Post subject: Re: Burn rates
PostPosted: Mon Jan 11, 2021 1:05 pm 
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A third thing that Burn Rates govern is Port Pressure at gas ports down-barrel in gas-driven autoloaders.

Any 2 otherwise identical loads (projectile and peak chamber pressure), the slower burning powder load will provide higher Port Pressure to the gas system than the faster burning powder does.

An overly fast powder CAN provide insufficient port pressure 12" down a barrel to cycle a gun, even at maximum chamber pressure. Pressure drop is too fast, gas bubble is too small.
On the opposite end, an overly-slow powder can produce EXCESSIVE port pressure, possibly high enough to damage the gun.
Example. The M1 Garand rifle, a reliable, and robust, war-tested, rifle, it's ammunition was designed around IMR4895, a "medium-rate" rifle powder.
In modern days, IMR4895 isn't "most optimal" for the case capacity of the 30'06 round, it is a little bit too fast, significantly slower IMR 4350 is very popular in it, better velocity with heavy bullets, not excessive chamber pressures, better (more) case fill.
For long-range competition Garand shooters combined the 2, decades ago, and the Port Pressure was so high that the long, unsupported, dog-legged, 2-piece welded, Operating rod, which pushes the heavy bolt and powerful springs open, was trying to operate too fast, and either bending or breaking, because Port Pressure was significantly higher than the rifle was designed for.

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 Post subject: Re: Burn rates
PostPosted: Mon Jan 11, 2021 8:09 pm 
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Oldstuffer, Boyle's law doesn't have anything to do with ballistics. It deals with a inert or ideal gas in a closed system, in other words it is pneumatics. It says the volume of an ideal gas (not burning) is inversely proportional to the pressure or P1V1 = P2V2!


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 Post subject: Re: Burn rates
PostPosted: Tue Jan 12, 2021 6:01 am 
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wrfish wrote:
Can someone explain to me how "burn rates" matter to reloading. I load 12ga with a several powders and 28ga with Longshot.I have Clays, International Clays, 700x,and Titewad and load 3/4 oz to 1 1/8, all target loads. What is important about burn rates?
Just trying to learn something.


They don't matter at all to reloaders, for burn rate charts don't agree, relative burn rates change places contingent on the application, and single / double base / triple base propellants are not directly comparable. All the burn rate charts warn that they are not to be used to determine loads.

Burn rate charts don't matter at all to a reloader who is using published, tested loads. Why would they? You either follow the directions, or you don't. Burn rates won't help you. A shotshell reloader is far better off paying attention to crimp depths than blankly staring at a burn rate chart: https://www.hodgdonreloading.com/reload ... shotshells .



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 Post subject: Re: Burn rates
PostPosted: Tue Jan 12, 2021 6:36 am 
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OldStufferA5#1911 wrote:
if you double the size of that fixed volume, the pressure will drop by 1/2.
Thus, every time that a bullet base (straight-wall cartridge) or wad gas seal doubles the distance from it to the inside base of a cartridge, pressure drops by half.


That relationship between volume and pressure only holds true if the gas is maintained at the same temperature during the expansion. The rapid expansion of the red-hot gasses behind the bullet essentially undergo adiabatic expansion and the pressure not only drops due to the increase in volume, but also due to the decrease in temperature so the pressure will be significantly lower than 1/2 when the volume doubles. Your gun is a heat engine and it converts heat into energy via gas expansion.

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 Post subject: Re: Burn rates
PostPosted: Tue Jan 12, 2021 7:21 am 
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Forget about burn rates and use published, tested loads from the powder source (Hodgdon, Alliant, etc.). They are safe, and the powder source has more "skin in the game", so can generally be trusted to be accurate.

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 Post subject: Re: Burn rates
PostPosted: Tue Jan 12, 2021 8:41 am 
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alliant extralite isnt in that chart.
i would put it very close to Ba10 by noblesporout.


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 Post subject: Re: Burn rates
PostPosted: Tue Jan 12, 2021 9:07 am 
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