Hi-
Just wondering if all powders burn in a "linear" fashion at different rates, or if there is acceleration, decceleration, or other nonlinear changes in burn as the burn progresses for some/all powders. In otherwords, can powders be engineered in such a way that they might start off burning half the powder really quick, then a slow burn of a portion for the next few milliseconds, then a quick burn at the end for the remaining bit... that kind of thing. Thanks for any insight!

Powder companies use four basic things to change the way powders burn.
1. The shape of the granules. flake powders burn faster and fairly linearly since they burn from two large flat surfaces that don't change shape much during the burn. Ball powders burn regressively as the surface area diminishes during the burn. Cylindrical powders burn regressively if they are solids, fairly linearly if they are simple tubes, and progressively if they have multiple perforations down their length (the surface area burning and producing gas actually goes up as the powder burns ).
2. During the manufacturing process, they can add more nitrate groups attached to the cellulose molecules by increasing the strength of the nitric acid and letting it work longer on the cellulose base stock. This raising the burning rate as more oxygen becomes incorporated into the powder.
3. They can add nitroglycerin (double based powders) which also incorporates more oxygen into the powder (nitroglycerin actually releases some free oxygen when it explodes).
4. They can apply coatings to the powder granules that slow down the initial burn rate of the powder. This is frequently done to ball powders to slow the burn rate; think H110/W296 or W748 powder.

They really can't design a powder that goes fast, then slow, then fast again as none of these methods enables such a design. Mostly they just try for a slow start, then faster and faster as this allows them to maintain the highest pressure level as the bullet goes down the bore a of a gun.

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1. The shape of the granules. flake powders burn faster and fairly linearly since they burn from two large flat surfaces that don't change shape much during the burn. Ball powders burn regressively as the surface area diminishes during the burn. Cylindrical powders burn regressively if they are solids, fairly linearly if they are simple tubes, and progressively if they have multiple perforations down their length (the surface area burning and producing gas actually goes up as the powder burns ).

That notion has circulated for a long time, but I doubt that it is correct. Think about it: You're saying that a large ball burns more quickly than a small ball. That's mistaken. It is not the total surface area, but the surface area as a ratio to the mass of the fuel. The smaller the granulation, the greater the surface area/mass ratio. That's why FFFFg black powder burns more quickly than FFg black powder.

No, the total surface area that's burning is the determinant of gas production. A powder with higher surface area to the mass of fuel is faster burning than one with a lower ratio of area to mass, simply because with equal masses of powder there's more surface area to burn in the one with the higher ratio.

With a given charge of powder, if there's no deterrent coating to slow the initial burning, the burning rate at constant pressure will be highest initially when there's more powder surface burning, then fall as the total surface area shrinks. Works that way for both FFFFg and FFg. The FFFFg burns faster, of course, because it has more surface area. But both are degressive.

Here is what Alliant is saying ;

Smokeless Powder: Combustible propellant that sits between the bullet and the primer in the case. On detonation, the ignited powder rapidly decomposes into a hot, forceful gas that instantaneously expands and propels the bullet out of the gun bore. The chief ingredient of single-base powder is nitrocellulose. Double-base formulas use nitroglycerin and nitrocellulose. Modern powders are a derivative of guncotton (nitrocellulose), which was developed and used in the 1800s in lieu of black powder because it produced less smoke and flash on ignition. To achive certain burn rates, powder grains come in different shapes and sizes. They can also have different surface coatings. Alliant Powder grains are made using an extrusion process and come in cylinder or disc shapes.

Now that being said ; Flake is generally the fastest burning powder ( Not always but generally ) . Then spherical or Ball which can be flattened balls also last comes tubular or extruded . More air around extruded or tubular which would have one believe it would burn quicker . How ever untrue , as it has a more restrictive coating so as to slowly build pressure curve .

It must be clearly understood that burning rates are not linear. There may be several powders which have very nearly the "same" relative quickness listed together, with the next listed powder being significantly different. It should also be understood that the burning rate of any given powder can vary substantially when different cartridges are being compared. Smokeless propellants are organic compounds, and are subject to lot-to-lot variations which are unavoidable during the manufacturing process. As a result, it is quite possible for a "fast" lot of a "slower" burning powder to appear to be somewhat "faster" than a "slow" lot of what would normally be thought of as a faster burning propellent. This situation, in effect, would cause these two powders to switch positions in the Burn chart. Bear in mind then, that these listings are subject to change depending on the particular lots of powder involved and a host of other variables which become part of the equation.

I forgot to mention this is why some burn charts vary as to what and which powders are fastest and slowest .

I don't know how to confuse any of you more .

Shoot Straight Know Your Target . ...

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Originally posted by Dr.K:
Here is what Alliant is saying ;

I don't know how to confuse any of you more .
:

Nice touch Dr. K, roger

Stonecutter

What I was saying is that a single large ball has more surface area at the start of the burn, when that single ball has burned for a while and become smaller, then it isn't producing as much gas because it is smaller, and has less surface area now burning. Yes, smaller granules are usually faster burning because they have more TOTAL surface area among ALL of the much more numerous granules than if there were larger, and much fewer, granules. But what we are talking about with regressive or linear is how the burn rate CHANGES as the powder burns, so the number of granules is fixed and the total area is diminishing versus staying almost the same as the powder burns.
One thing that I hadn't mentioned before, is that nitrocellulose burns faster the higher the pressure levels that are upon it. And powder companies use this along with coatings to help "tune" their powders for certain pressure levels. So if one company tests someone else's powder for burn rate using a different pressure level than what the powder is "tuned" for, they are going to get a different burn rate than the manufacturer.
Unique powder really is unique as it burns well at virtually any pressure level. Used in shotguns as low as 8,000 cup, handguns from 10,000 cup to 36,000 cup, and in rifle loads up to 50,000 cup. On the other hand H110/W296 with a very heavy coating designed to slow the burn rate will fizzle if pressures don't quickly go over 25,000 cup; that's why powder manuals have warnings about not using reduced loads with this powder. Every powder really is different, and each has an intended application that it was designed to handle.

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Originally posted by Gaillo:
Hi-
Just wondering if all powders burn in a "linear" fashion at different rates, or if there is acceleration, decceleration, or other nonlinear changes in burn as the burn progresses for some/all powders. In otherwords, can powders be engineered in such a way that they might start off burning half the powder really quick, then a slow burn of a portion for the next few milliseconds, then a quick burn at the end for the remaining bit... that kind of thing. Thanks for any insight!

This would be great if you could do it. You should start developing it. You'd be rich! I'd buy it, after it was proven.

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Originally posted by Gaillo:
Just wondering if all powders burn in a "linear" fashion at different rates, or if there is acceleration, decceleration, or other nonlinear changes in burn as the burn progresses for some/all powders.

Hey Gaillo, Powder can exhibit every trait you mentioned. It is impossible to give you a single answer, because Load Density, Burning Rate, Case, Primer, the specific Powder being used(some are more erratic than others), Bullet, Bore Dimensions and Surface Condition, plus the Chamber Dimensions - all - contribute to how well the Burn Sequence occurrs.

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In otherwords, can powders be engineered in such a way that they might start off burning half the powder really quick, then a slow burn of a portion for the next few milliseconds, then a quick burn at the end for the remaining bit... that kind of thing.

If an idea can be generated, usually the process can be created with enough time, money and effort.

In the specific issue of Powder, I do not believe what you are asking is currently available. It would require making a specific Burn Rate of Powder and then adding additional layers of separate Burn Rates to it. This would be different from simply changing the amount of Surface Area and adding Deterrent Coatings which is the current process. And it would require being able to Ignite every grain at the exact same time which is impracticle with the existing Primer Ignition at the end of a Case.

There are some folks that experiment with Duplex and Triplex Loads with various Burning Rates of Powder. This has the potential to accomplish what you asked, in a different way. But it can be extremely dangerous if the Load isn't exactly correct or if the layers shift slightly within the Cartridge.

Generally speaking, there is an abundance of excellent Powders on the shelf for all common Cartridges. And for most of the real old Cartridges that can be difficult to locate Cases for. That said, there are areas of the world where all the Powders are just not easy to purchase.

Best of luck to you.

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Originally posted by CMcDermott:
So if one company tests someone else's powder for burn rate using a different pressure level than what the powder is "tuned" for, they are going to get a different burn rate than the manufacturer.

Yes, and in actual loading practice powders will have different burning rates, including changing relative positions on the burning rate scale. I've just been looking at loading manual loads for .38 Special and .45 ACP and noted several instances where Red Dot maxes out at a lower charge weight than Bullseye with similar pressure. Alliant's website says that Red Dot burns 94% as fast as Bullseye. So you'd expect you could always load a charge weight known to be safe with Bullseye of Red Dot and be sure the pressure would be lower. Doesn't work that way, though. Apparently Alliant's bomb test for burning rate doesn't well reflect the burning conditions in these handgun cartridges. (Red Dot's primarily a shotgun powder, in which application it usually wouldn't be burning at over 11,000 PSI or so, rather low for pistol cartridges.) Just one example of many if you look closely at published loading data.

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or if there is acceleration, decceleration, or other nonlinear changes in burn as the burn progresses for some/all powders.

Within a range of pressure levels, the powders increase pressure and velocity in a linear, predictable fashion as more powder is added.] However, this phenomenon changes in a non-linear way from pressure range to pressure range, and these changes are different for different powders. Double-based, particularly spherical, powders seem more susceptible to such problems. For example, I once was attempting to work up to the highest velocity I could achieve using 120-grain bullets and WW760 powder in the 7X57mm Mauser. I got up to around 3110 FPS. Then, at that level, additional powder gave little measurable velocity increase, even though pressures were getting prohibitive. Any powder increase beyond that point resulted in LOWER velocities, and unacceptable pressures...... so I concluded that even 3110 FPS with those bullets and 760 powder was over max in that particular 7X57mm.....

Powders can also exhibit different apparent burn rates according to the size of case they are used in. The best example I know of is that of the very similar H-335 and BL-C2. These powders have such similar burning rates that they are frequently listed adjacent to one another on burning rate charts, with some listing one as the slower and some listing the other as the slower.

When you look at their performance in a .222 or .223, indeed they are very similar for the most part, with H-335 sometimes seeming slower. However, if you will look at them in a cartridge like the .416 Rem or .458 Win, you'll find that H-335 tops out several grains before BL-C2 in most loading manuals. I have no explanation for this phenomenon, but it surely exists and is a function the the arcane world of interior ballistics.

Ricochet ; If you like using shot shell powder for pistols and have not already tried this one , Please do so H Clays . This seems to be a even pressured powder at low weight or better put lower charge weight . Do you have any loading data on it ?. If not I'll dig up some for you .

I used it and liked how clean it burnt gave decent accuracy as well .

Powder can be a strange animal as well as unpredictable at lower as well as higher volumes in different calibers loadings .

Even the most experienced of us need to consult a reputable loading manual JUST TO BE SURE , then proceed with caution .

I never figured an extra 22 fps velocity was worth my weapon nor my life !. It's surely no more accurate !.

Shoot Straight Know Your Target . ...

Shoot Straight Know Your Target . ...

There's Clays data for several of the pistol cartridges I load in the Lee handbook. I have yet to pick up any Clays, but it looks like useful stuff.

I've used a fair amount of Nitro 100 and still have some I'm using up. Published data for that has changed drastically in some cases, to lower charges. I found some of the .45 ACP Nitro 100 data in the Lee 2nd Edition book to be too hot in my .45.