Powder Volume Vs weight

[jim8115]

This is something I have never tottaly understood.......
Ok, everyone says weighing is the most accurate way to measure powder, because volume weight can change with temp/humidity changes.Thats why manuals give specs in Grains. Here is what I dont understand.... Assume I scoop out .5cc of powder, and it weighs 5.0 grains. I leave that exact powder on the scale, and tomorrow the temp/humidity changes enough that now it weighs 4.8 Grains ... it is the same powder from the day before, but now I have to add .2 grains to get the same result? That same volume of powder should have the same energy as it did yesterday, regardless of temp/ humidity..........Can someone please make me understand?

[mehavey]

This is [one of the reasons] why different batches of reloaded ammunition often exhibit slightly different velocities from each other.

Don't worry about it (or try to chase compensating for it).
You'll drive yourself nuts.

[Lost Sheep]

jim8115,

You have hit upon one of the devilish controversies in the loading world. Volume vs Weight.

Loading manuals give charge weights because the scale is more universally found, easier to calibrate more reliable/repeatable than a volume measure. That last point is because some people will pack a measure more densely than others ("Some settling may have occurred" is a phrase often found on the packages of breakfast cereals, powder kegs, laundry detergents, etc.) Some people may mound up their measure and some strike it off level. Considerable variation in the amount of powder can be produced by different person's technique of filling the measure.

However, many high-accuracy long-range benchrest shooters claim (and there is considerable evidence that this is true) that volumetrically measured charges do give more consistent results than weighed charges. Provided the volume measure is filled with consistent technique, but - here's the rub - EVEN IF THE WEIGHT OF THOSE CHARGES ARE DIFFERENT.

I don't make the opinions, I am just reporting.

Sorry, I can't cite time and place, but there is a master shooting class that annually demonstrates the amount of variation (as shown on-target) of ammunition loaded volumetrically vs ammuntion loaded by weight. Volumetric wins every time.

I can't explain it.

I expect someone to someday suggest using neither method. Instead, count granules.

7.0 grains of Unique is exactly 1,856 granules.

Lost Sheep

P.S. Humidity can make a difference. Have you ever heard of water injection? The energy derived from an internal combustion engine can be enhanced by water in the combustion mix. It has to do with the amount of energy released by the water condensing instead of remaining as vapor. I can believe also that the amount of water in my powder will affect the burning rate and energy released. Does dry wood burn differently than wet wood? I recommend you keep dessicant in your powder.

[Sport45]

I think Lost Sheep nailed it.

Except I get a different count for granules of Unique per grain and believe the water helps mainly by evaporative cooling of the engines charge air.

[dahermit]

... believe the water helps mainly by evaporative cooling of the engines charge air...

Or, is it the water turning to steam in the cylinders and increasing the the pressure?

[wncchester]

Volume vs. weight? We buy sugar by the pound, gasoline by the gallon, neither is a 'better' method than the other. Not a problem, use your powder scale so you can match the weight your loading books say to use.

[Doyle]

Another REALLY good reason to keep your powder sealed tightly between uses. When you are done with your reloading session, put all your loose powder back in a sealed container.

[sundog]

Everyone has their own opinion and know what works for them.

Here's another take on the WHOLE thing: the Houston Warehouse

[Mike Irwin]

The great thing about modern smokeless powder is that it's virtually impervious to water and weight changes due to humidity. It may take weeks or even months for a sample of powder to gain or lose water weight. And, due to the nature of nitrocellulose, the amount of water weight it will gain or lose is a very small faction of its overall weight, on the order of half a percent or less.

[PA-Joe]

All of the powder measures with the exception of those new automatic electric ones are based on using a fixed volume to drop the powder charge.

The problem comes when you try to use the weight and volume tables, or you change powder batches. You will notice that most of these tables are incorrect and dropping light.

Each batch of powder has a different weight to volume ratio so each time you use a new can of powder you have to re-check the actual weights and make a new table.

That is why you need a good check scale and set of check weights.

Don't assume that the spoons you used the last time and the measure settings you used the last time will drop the same weight the next time you use them.

[serf 'rett]

This stuff makes my head hurt and Lord preserve me if I must start counting Winchester 231 flattened ball and Power Pistol flakes.

For some interesting reading on the weight vs. volume debate, you may like taking a look Richard Lee's epistle in the Lee Reloading Manual.

[serf 'rett]

Staffer Mike - thanks for the note on weight changes/water absorption, but I note you mentioned modern powder. That makes me wonder about the approximate 2.5 pounds of W-231 a coworker gave me last week. Is the powder modern if it’s in a Winchester-Western steel can marked 3 pounds. How long has it been since that powder was sold in 3 pound cans?

But I’m digressing from the opening post…

[PawPaw]

Volume vs weight. Here We Go!

Powder is hygroscopic and can absorb water, which has weight. However, 0.5 cc is 0.5 cc everywhere. Even in Texas.

That said, I weigh my rifle charges and throw my pistol charges. I've got one powder measure permanently set to throw 4.6 grains of Bullseye. I check it occasionally to make sure that the grandkids haven't been fooling with it, but it's always the same. 4.6 grains.

There's a lot of science and mythology on the subject, but I would suggest that the biggest manufacturers of ammo don't weigh every charge. They use volumetric measures.

Still, I weigh rifle charges. Go figure.

[Mike Irwin]

"Powder is hygroscopic and can absorb water."

Nitrocellulose is moderately hygroscopic, but that property is greatly modified by other chemicals that are added to it (or are used to coat the grains) during the powder making process to the point where it is, for all intents and purposes, it is largely
non-hygroscopic.

This is an old reference, sometime in the 1920s, I believe, but by then many of the powders that we have today were already in production.

http://www.freepyroinfo.com/Pyrotech..._Chapter_6.pdf

The section of the hydroscopic qualities of nitrocellulose-based powders begins on page 313.

The ball powder manufacturing process was introduced by Olin Corporation in the 1930s, and if anything it provides a powder that is even more resistant to moisture absorption than extruded-type powders.

[PawPaw]

Originally Posted by Mike Irwin

Nitrocellulose is moderately hygroscopic, but that property is greatly modified by other chemicals that are added to it (or are used to coat the grains) during the powder making process to the point where it is, for all intents and purposes, it is largely non-hygroscopic.

This is an old reference, sometime in the 1920s, I believe, but by then many of the powders that we have today were already in production.

http://www.freepyroinfo.com/Pyrotech..._Chapter_6.pdf

The section of the hydroscopic qualities of nitrocellulose-based powders begins on page 313.

The ball powder manufacturing process was introduced by Olin Corporation in the 1930s, and if anything it provides a powder that is even more resistant to moisture absorption than extruded-type powders.

I stand corrected. Powder doesn't absorb moisture.

[Jimro]

The science of "internal ballistics" is all about turning a solid into a gas.

It is easier to measure solids by weight (mass), and easier to measure gasses by pressure (mass, volume, and temperature). Conservation of matter tells us that the same MASS of powder will equal the MASS of the produced gasses (N2, CO2, H2O for complete combustion). To get the same pressure then projectile needs to have the same resistance (friction) to the bore as well as resistance to force (mass), the brass needs to have the consistant internal volume as it stretches against the chamber walls, and the burn rate needs to match presicely.

Simply put, to make accurate ammunition you want the "pressure curve" of each round to be as similar as possible to every other round you put through your bangstick.

I find that my best accuracy is found by getting 95% or more case fill, (volumetric) and then weighing that charge (mass). Normally this method identifies early on in the load development process an "accuracy node" that doesn't push beyond the max load in the reloading manual (if you are using a powder with a burn rate appropriate for the caliber and bullet weight combination).

Part art, part science, part mystery. And this is just "internal ballistics", not even talking about external or terminal ballistics...

Jimro

[Unclenick]

"First contemplation of the problems of Interior Ballistics gives the impression that they should yield rather easily to relatively simple methods of analysis. Further study shows the subject to be of almost unbelievable complexity." Homer Powley

Simple in principle but not in practice. The problem is the bullet is moving when the pressure peak occurs. So, if the timing of the pressure peak isn't exactly the same from one shot to the next, the bullet isn't in the same position from one to the next. That means the expansion of the powder space behind the bullet isn't the same, so the volumes the pressure peaks in aren't the same, and that changes both the pressure peak value, which affects the ballistic efficiency, and with it, the final velocity of the bullet at the muzzle. In a gross comparison, that is why putting the same weight of same energy density fast and slow burn rate powders behind a bullet don't produce the same peak pressure and velocity.

So, whether or not the peak occurs at the same point in bullet travel down the bore depends on the powder burning characteristics being the same from one shot to the next. And that's where the volume vs. weight problem gets its start.

Take a look at the image below. All three are of the same case filled with the same charge; the exact, actual same charge, poured back out and re-filled for each photo. The difference is the first is poured in with a funnel with a short spout. The next has a spout extension (drop tube) a few inches long. The last one has a drop tube three feet long. See how the bulk density is changed?



When the grains are packed more closely together, the flame front and hot gases have a harder time moving between the grains and lighting the powder. The result is a slower starting burn rate in the more dense packing. Hatcher's Notebook (pp. 312-313) has an example of a powder with long grains that could only be dispensed to within a spread of 1.7 grains my the Frankford Arsenal loading equipment producing better accuracy than a similar burn rate short grain powder that could be dispensed within a spread of 0.6 grains. The coarse grain powder apparently self-compensated for its load density when it packed tighter by its starting burn rate being reduced by just the right amount. As a result, if the powder falling into the measure cavity were more densely packed than a previous charge, it could produce about the same barrel time and velocity. The long grains probably also kept the load density structure better locked in place when it was moved around later, especially if the load was slightly compressed.

That example also shows that this property isn't the same for all powders and grain cuts. Some may produce better accuracy by volumetric measure (especially when you are loading at the bench, so this isn't changed much in transport) and some may do better by weight. I find IMR 4064 tends toward being one of the former, as an example, making a great powder measure powder.

[mehavey]

Out of curiosity, UncleNick, does vibrating down the powder in a filled case (using the blunt chuck edge of hand engraver) produce a similar packing to that of a long tube?

(To avoid powder "crunch" I'll often use it to drop the level of a literal case-full to near the mouth down to well under the neck on powders like 4831)

[Mike Irwin]

Yes, vibration can certainly seat powder in the case. Years ago I read of a guy using the motor out of an old electric shaver for that purpose.

[Unclenick]

Yes, it works. And this opens another whole can of worms. I remember reading (can't recall where) mention by a fellow that he'd discovered a maximum load that worked just fine when he put it together at home, but that would produce high pressure signs if he rolled the same load at the shooting bench. He finally worked out that his powder was packing down due to transportation vibration when it came from home to the range. It was burning both faster and at higher pressure for being fluffier when loaded at the range. His powder choice obviously was not compensating for being fluffed up in his chambering.

A couple of guys have talked about setting their loading tray on a fish tank aerator pump and letting it shake charged cases down. One fellow spoke of putting his rounds on top of his vibratory tumbler. I think he had put a hole through a piece of plywood that replaced the lid when he did this. He probably had some molding glued to it to keep the boxes in place, but I don't recall the details. I also don't recall if this was charged cases or finished rounds being uniformed or if he was just making room for more powder in lieu of conventional compression.

I think it's hard to beat drop tubes for load workup at the range. You can get the packing without a source of electricity for a vibrator. That and a chronograph lets me look for a powder that shows the least variation in MV going from tight pack to loose and fluffy. That's going to give the best immunity to field conditions or other variable handling history for the finished loads.

[TXGunNut]

Before I got my drop tube I got similar results by touching a charged case to the rim of a vibratory case cleaner for a second or two. I've only done it with BP but is was dramatic how much the level dropped. Will have to use my drop tube next time I load a compressed load, I don't like to crunch powder.
Back on topic I'm fascinated by the volume vs weight debate but I think equipment and technique are the limiting factors here. I don't have a volumetric measure that I feel I can use to throw a consistent load of stick rifle powder. Of course, I'm using a scale to check for uniformity so my methodology is likely flawed. I guess I'll continue to weigh rifle charges and throw pistol charges, especially since I invested in a Chargemaster last year.

[Jim243]

Can someone please make me understand?

No, you have to do that. For the last 500 years ALL powder measures dispense VOLUME, weither it is a powder horn or a Lyman 55. You will despense a certain volume and then weigh it and adjust the measure to get the VOLUME that matches what you want in weight. Will it weigh the same tomorrow morning? Maybe, maybe not. As long as all cases where loaded with the same volume of powder, consistant results will be obtained. That's why benchrest shooters load at the bench, consistant results from shot to shot under the same conditions.

I would trickle charge all my rifle loads on a scale to get what I thought was a more consistant results. (I do not load at the bench). Since I am OCD, I too went with the RCBS ChargeMaster 1500 for all rifle loads, I have now come back to a straight drop from a powder measure (Lee Pro-Auto Disk) and do not worry about weight that much any more for 223. All other calibers get the ChargeMaster treatment. (sitll OCD)

Most if not all powder will settle in the case just by sitting on the shelf or in transportation that is why you need to test each batch of reloaded ammo each time you go to the range. Will batch to batch of ammo give the same results, we like to think so, but that is not always the case since conditions change from keg of powder to keg or powder as well as conditions (temp, humidity, barametric pressures) between reloading secessions.

If it was easy, there would be no fun in reloading and we all would just buy commercial ammo. (ya, like that's going to happen)

Stay cool, keep your powder dry and keep working on that PERFECT load.
Jim

[WESHOOT2]

Volume for making many.

[Hook686]

That same volume of powder should have the same energy as it did yesterday, regardless of temp/ humidity..........Can someone please make me understand?

No, no one can make you understand. However since the energy per unit volume has changed with the temperature and humidity to keep the same total energy as previously, the volume must change. Why would you assume that the total energy of the load used in the previous session was the more accurate loading ? The actual total energy released is based upon a vast array of variables. Temperature and humidity are but two. I figure the force used to accuate the reloading press handle is more of a variable than the temperature and humidity variances.

Don't sweat the small stuff. Start low and work up. I avoid maximum loads.

[jim8115]

I guess my question was more for theory than practice. For example, if i load x grains(Weighed) today when temp/ humidity is 70/30, will those loads shoot the same as some loaded when the temp/humidity was 90/70 ? or would loads loaded by volume those two days shoot more consistent.