I have mentioned this before, but I thought I'd go a head an start a thread on the subject in case anyone was "searching" for something on the topic.

The issue at hand is the difference in density (bulk density in this case) between lots of the same powder. I probably should define a couple of terms to start with.

Density = Mass per unit volume - is the formal definition. Let's not get hung up on "mass" versus "weight". Technically, "mass" is independent of gravity, where "weight" is dependent on gravity. For example: A dumbell that weighs 10 lbs on earth would weigh about 1.7 lbs on the moon. That same dumbell would have a mass of 4.54 kilograms on earth and the moon (or in "British" units, 0.311 slugs). This independence from the effect of gravity is why scientists and engineers prefer "mass" to "weight" because it relieves them of the task of calculating "weight" as a function of variations in gravity. HOWEVER, we all do our shooting on earth, so weight is just fine for our purposes.

"Bulk" Density - This is the density of a material that is commonly used in "bulk" but occurs in tiny pieces - like gunpowder. We use thousands of "pieces" (the granules) of gunpowder in a single charge. One granule of the powder has a specific density, (as defined above), but one grain, (weight grain), of the powder has a different "bulk" density due to all of the "air" between all the individual granules of that one grain. Put another way, if we had a grain, (weight), of solid gunpowder, we could measure it's density because that one grain, (weight), would occupy a specific volume. But since one grain, (weight), of powder will contain many granules, the one grain, (weight), of powder will occupy a larger volume. Therefore, its "bulk" density will be less than its "solid" density.

So.. what does this mean to us handloaders?

Since the easiest way to determine the "proper" charge for a specific cartridge is to weigh it, that's what we do. Hence charges are reported usually in "grains" of gunpowder. (The unit "grains" - one seven thousandths of a pound - is an entirely separate issue. ) However, we weigh them, only because this is easy for the "regular Joe" to accomplish, because it's easy and cheap to buy scales. It's NOT easy OR cheap to procure the equipment to measure density - mass per unit volume.

HOWEVER, when we take the "easy" path, we give up some 'control' because we have to make some assumptions. The biggest of those assumptions in this matter is that the "bulk" density of the powder in question is always the same. That assumption, while useful, and for the most part necessary, adds variability to our results. The key to understanding why, lies in the fact that gunpowder has a characteristic described as "energy density". (There's that "density" term again.)

Energy Density is the amount of chemical energy (usually reported in units of Joules or Watts) per unit density. So for example, Vihtavouri Oy, (being the ONLY manufacturer that reports their powder's energy contents), says that N-150 has an energy content of 3750 Joules/gram. They report that the bulk density of N-150 is 0.910 grams per cubic centimeter. Therefore, one can calculate what the energy content of a specific load is. This is important relative to case capacity (volume), and projectile mass (weight). The significance of this is that all those "weights" eveyone uses to determine "appropriate" charges are based on the assumption of a uniform, and constant, "bulk" density figure for a specific powder. That assumption is weak.

Manufacturing processes, no matter how precise, cannot produce EXACTLY the same energy density from lot to lot of powder. They just can't. Furthermore, the age of the powder, (time since manufacture), also effects density, which in turn effects "bulk" density. What this variability means, is that one man's 50.0 grains of N-150 might very well contain more chemical energy than the next man's 50.0 grains of N-150. So exactly how big a deal is this really?

Is it just an exercise in meaningless precision? A tempest in a teapot?

I'll provide some numbers, and let you decide for yourselves.

Where this comes into very clear view, is in the use of QuickLoad reloading programs. Each powder is described in very specific detail regarding its burn characteristics, and its "solid" and "bulk" densities. This is so, because QL uses multivariate equations that require specific powder information in order to precisely and accurately estimate muzzle velocites, chamber pressures, and many other internal ballistic outputs. (This is why, by the way, I always ask people to measure the volume of their cases when they want me to work up preceise QL loads for them.) So what actual, practical effect might lot-to-lot differences in a powder's "bulk" density make?

Some of you may remember the difficulty I was having trying to find a precise load for the .338 MAI Ol' John made for me. QL had I3031 as the powder that provided the most velocity for the least pressure. However, I was "all over the place" when trying to work up loads. Finally, I got a load that was "good eough" to take to Colorado on a deer and elk hunt. You may also remember, that when Hunterbug shot the first round down in Colorado, it blew a primer. The primer literally fell out of the case. It wasn't a fluke.  When I test-fired the rifle, it did the same thing. For the life of me I couldn't figure out what was wrong. I KNEW the loads weren't "hot". To make a long story shorter, that batch of powder was probaly 20 years old. While it was "fine" chemically, I am quite certan that it was considerably less dense than "new" powder. What that meant was that a 50 grain charge of "old" powder had WAY more energy than a 50 grain charge of "new" powder because the density of the old powdr was WAY less than the desnity of new powder.

As a result of that series of events, I made for myself a device for measuring the bulk density of gunpowder. It's simple really, just a "tube" of known volume with a little base on it so it stands up. I fill it with the powder in question; pour the powder onto my scale and weigh it; then divide the weight by the volume of the tube.

So here's a specific example using Vihtavouri's N-150. The bulk density according to QuickLoad is 0.868 grams/cc. According to their reloading manual, the energy content is 3750 j/gram. So, 50 grains of N-150 would have a chemical energy content of 12,152 Joules, (50 grains/15.43 grains/gram * 3750 j/g). Now when I measure the bulk density of the N-150 I have on hand, I get a figure of 0.812 grams/cc. A difference of about 7%. So when I weigh out 50 grains of my N-150 - because it is lighter than new N-150 - I actually put about 7% more energy in that 50 grain charge because it takes more of my "light density" N-150 to equal the weight of "normal" N-150. What that means is my 50-grain charge is the equivalent, energy-content-wise, of a 53.7 grain charge of "normal" N-150.

Now let me assure you the "lightness" of the bulk density of my N-150 isn't because it's "old". It's only about a year old. It IS because it is a different batch.

It is not my intent to scare anyone. This difference I have measured is the greatest I have measured so far. Most of my other powders are within 3% or so.

On a practical note, let me offer a simple way to check your powder batches. Take a cartridge case - the bigger the better, but even a .45 ACP would work. Fill it with the powder in question. Fill it right to the top to the point that you have to use a straight edge to level off the excess. Weigh that caseful, and write down the weight on the cannister. Then, when you get a new batch of that same powder, do the same thing and compare the weights. If they are the same, then your "pet loads" will continue to work as they always have. However, if there is a difference, then you'll need to adjust your charges to reflect that difference. Using the N-150 example above, I would adjust my "normal" 50-grain charge down to 47.8grains. That would give me the same chemical energy content as my "new powder" 50-grain charges did.

Paul

Wow!  I understand that now.  And I don't even have a headache afterwards.  :D  Thanks Paul!

QuoteAnd I don't even have a headache afterwards.

I'm glad. I knew it was a bit long, but I wanted to try to make sure the practical aspects were covered, not just the theoretical ones.
 
When the variability between the case volumes, (even those with the same headstamp and from the same batch), and the variability of energy density between lots of powder is taken into account, the fact that we can ever shoot tiny groups is a bit surprizing. It points to the "robustness" of the "system".
 
Actually, I did want to explain why the bulk density of a given lot of powder will change over time.
 
It is NOT a chemical degradation.
 
Nitrocellulose, (to put a "general" name to the complex compound today's powders are), is a fairly stable compound when compared to MANY other commonly used compounds. Based on personal experience and opinion, I'd say the shelf-life of nitrocellulose "gunpowder" - when properly stored - is at least one human life-time, and maybe considerably more. If the powder gets even damp however, it degrades immediately. "Damp" can mean just high humidity.
 
If that seems to fly in the face of my own observation regarding the cannisters of I3031 I mentioned above, let me explain.
 
When powder is manufactured, a few chemicals used as "carriers" and as "driers" are added. (For example, one of the driers is ether.) During standard manufacturing processes, these carriers and driers are evaporated off. In the finished product, they are technically "gone". By necessity, that "technically gone" has a practicality to it. Manufacturers cannot wait "forever" for "all" of the carriers and driers to evaporate off, so an "acceptable" level is allowed in the final product.
 
These volatile chemicals, (volatile = "evaporates at low temperatures"), are readily apparent to your nose when you open a new cannister of powder. However, if you use that powder sparingly, AND if the cannister in which it is contained isn't pretty seriously air-tight, these volatiles will continue to evaporate, and every time you open the cannister, that amount of the volatiles that have evaporated into the air space above the powder escapes. Not only does what is in the air above the powder escape, that escapement "makes room for", (in chemical terms, "lowers the partial pressure") of those compounds in the cannister, making "room" for more of the compound to evaporate out of the granules of powder. This makes the powder more and more energy dense. Every time you open the cannister, you change the bulk density (and therefore the energy density), just a tiny bit. The longer you keep the powder, and the more you open the cannister, the more it will change.
 
This is why I have mixed emotions regarding 8-lb "kegs" of powder. On one hand, an 8-lb keg ensures that all the powder came from one batch. However, if that powder isn't loaded into cartridges, (which is the absolute BEST place to "store" powder), fairly quickly, opening and closing the container, will over time increase the energy density of that powder.. So for me, 8-lb 'kegs' are great for pistol cartridges in which it might be possible to use 8 lbs in less than a year. But for rifle cartridges, for which even a single pound might last several years, an 8-lb keg would definitely need to have its bulk density monitored. "Monitoring" just means performing the "case full of powder" exercise about once a year.
 
Paul

a question..  if you decrease the amount of powder used by a percentage will you also decrease the chamber pressure.  which would in a round about way change your velocity.

I wish there was a simple answer to that question b-bob. Actually, there is: "Yes". Unfortunately, that isn't the complete answer, and with it, you cannot predict reality.
 
When the volume of the charge is reduced, the volume of the "combustion chamber" is increased. Because gunpowder's burning characteristics are a function of the pressure in which the powder is burning, increasing the volume of the combustion chamber should slow the burn rate thereby reducing the max pressure, and thereby reducing the muzzle velocity. HOWEVER...
 
We're back to the TRUE issue which is the relationship between weight and volume. As you've noted, the volume of the combustion chamber is reduced, but... the energy density has not been reduced. Remember, the real issue was the fact that the weight of the charge had to change, not the volume. Of course when we reduce the weight, we reduce the volume, but not by the SAME amount.
 
Reducing the weight of the 50-grain charge by 3.5 grains (about 7%), does NOT reduce the combustion chamber buy that same 7%. Put mathematically, the effect on pressure is not linearly corellated to a reduction in charge weight if hte energy desnity remains the same.
 
The combuistion chamber volume went down by, I'd guess, less than 1%. As a result, there is almost no detectable - at least by me - reduction in muzzle velocity because the energy density of the charge remains the same. So in effect, we have the same amount of chemical energy available, but we're going to burn it in a combustoin chamber that is only very slightly larger. Therefore, we're not likely to be able to detect (measure) a difference in MV.
 
Also keep in mind, that 7% is the largest discrepancy in bulk density I have so far measured. Most are half that or less, which further reduces the amount the combustion chamber is increased.
 
Paul

So then in measuring case capacity in grains (or cc's) of water, one should weigh the case and bullet, then:
1)leave the primer out
2)seat the bullet to shooting depth
3)fill the case through the flash hole and weigh?
4)subtract the weight of the un-assembled components
Correct?  
Or do you want the water volume in cc's?

Brings up another question...........
 
           I`ve noticed different powder is shaped differently.   Would finer grain powder ignite faster than corser  grain??  My thoughts are yes.  That said finer grain powder will `pack` tighter leaving more room for additional powder..........  ?
 
   In reloading .308 cartridges some books call for maximum load of MR at 45.5 grns and another book lists 47 grns.   Yes, 47 will fit but it`s pretty tight behind the Spitzer that I use. In general  some cartridges sound pretty loose when shaken, some loads are quiet( tight ).  I notice a BIG difference in the `sound` between 45 and as little extra as 45.5 grains.

Back in another life I shot long range .308 competition. The Rod and Gun club had a state of the art Chrony and we had a 500 yard range to play with. All the brass, powder, bullets etc were provided for the team of which I was a member. Thats when I/we discovered IMR4064. Our largest deviation with this powder was less than 30'/sec. No other powder we tested was less than 50'/sec in 5 rifles. I do not know whether density has anything to do with this and it certainly is not based on any scientific data just raw numbers. I have been a 4064 fan ever since. I usually don't have to worry about "old powder", that said, I used up the last of the 30 pound keg of W 452AA about 3 years ago....Bill Thibeault will remember as I won the MEC reloader and powder on a coin flip in 1978? :D Regards, Rick.

Jamie.270 - Too complicated.
 
Forget the bullet.
 
Leave the primer in.
Don't resize.
Weigh empty case.
Fill with powder of choice.
Weigh full.
Subtract empty case weight from full case weight.
 
That's that case's capacity with that powder. Do the same thing in a year, and see if the casefull of powder weighs the same using the SAME case. If not, you might want to adjust your charges accordingly. Or...
 
Instead of trying to keep track of that case for a year...
 
Weigh an empty, fired, case (with spent primer in).
Fill with powder of choice.
Weigh.
If interested in other powders, repeat the "fill and weigh" sequence with each one, recording the filled weight for each powder.
Now, fill with water and weigh again.
Subtract the weight of the empty case from the weight of the "wet" case and each of the powder-filled.
 
The difference between the case's weight dry and empty, and it's weight "wet" is the case capacity in CCs. NOW, if you divide the weights of the powders, by the weight of the water, (the case capacity in CCs), you will have the bulk density for each powder. With that information, you could throw that specific case away if you wanted, perform the same sequences of "fill and weigh", and the bulk density figure would be the same.
 
Let me give an example with "real" numbers.
 
The weight of an empty case is 150 grains.
The weight of that case full of I4064 is 206.17 grains.
The weight of that case full of water is 213.61 grains or 13.498 grams.
Therefore, the weight of the I4064 is 56.17 grains or 3.640 grams.
The weight of the water is 63.61 grains or 4.155 grams.
 
Now, dividing the weight of the powder, by the weight of the water, gives 63.61 grains / 58.28 grains = 0.883 (the units cancel out). Dividing using the metric units gives 3.640 grams / 4.155 grams = 0.883. Again the units cancel.. HOWEVER, there is a "truth" we have yet to employ... 1 gram of water weight equals 1 cubic centimeterof volume, therefore, we can divide 3.640 grams of I4064 by 4.155 CCs of water, and get a bulk density of 0.883 grams/cubic centimeter or 0.833 g/cc as the bulk density of I4064.
 
Armed with that figure, you can use ANY container to determine if the bulk density of your powder has changed over time, or even if the bulk density of the new batch you got is different from the old batch you just finished.
 
JaDub... You are correct. The size and shape (ball, extruded, flake), of the powder determines it's "bulk" density. Its shape is precisely why its "bulk" density isn't the same as its density. And yes, the finer the granules, the less air - more packed if you will - the powder is when it is in the case.
 
Rick - I think your experience with the .308 and I4064 is precisely because the "stars line up just right" with I4064, the .308 Win case capacity, and 24" barrels. It is one of the powders with which it is easiest to get the Optimal Charge Weight and the Optimal Barrel Timing.
 
Paul

I'm sorry Paul, I meant the case capacity measurement you referred to in the thread starter here:

QuoteThis is so, because QL uses multivariate equations that require specific powder information in order to precisely and accurately estimate muzzle velocites, chamber pressures, and many other internal ballistic outputs. (This is why, by the way, I always ask people to measure the volume of their cases when they want me to work up preceise QL loads for them.)

Sorry for the mixup. :~(

That's what I was referring to also Jamie. It's that case capacity - the 'wet' case weight minus the dry case weight - to which I was referring.
 
QL has been able to provide some very close estimates of muzzle velocity for a couple of folks that had good measures of their case capacities. However, some folks' scales don't have enough dynamic range (smallest weight to largest weight), to handle a case fill of water. In that circumstance, I suggest that they simply fill the case with the powder of choice, pour the powder onto their scale and weigh it, then using QL's bulk density figure, I can get close to the actual case capacity.
 
Paul

Hmmm, that's odd.  I would think the lost capacity from the bullet's protrusion into the case would be significant.  Does QL calculate this based on known bullet length, shape and COAL?

Quote from: Jamie.270;92263Hmmm, that's odd. I would think the lost capacity from the bullet's protrusion into the case would be significant. Does QL calculate this based on known bullet length, shape and COAL?

Absolutely.
 
Paul

Here are a few pictures of what I call QuickLoad's "Front Page". It is the input and output for a specific cartridge and load.
 
First, the bullet and case input. Notice the:
 
Maximum case capacity, overflow.
The volume occupied by seated bullet.
The usable case capacity after bullet is seated to specified depth.
 

 
Notice that in the bullet seating depth area, the "shank seating depth" is different than the "seating depth". That's due to the calculations based on the length of the boat-tail.
 
Here is the powder input:

 
The parts that are "grayed out" cannot be changed from this page. I'll show where they get changed next. Notice the "Propellant Solid Density". This is NOT the bulk density. Bulk density determines the charge volume. Solid density determins the energy density based on the factory's values for the joules of energy per gram of powder.
 
Here is where one would change the burn characteristics for a given powder. A very risky business if you don't know what you're doing. I do not fiddle with anything but the bulk density figure, which is the subject of this thread.

 
Note the solid density of 1.610 g/cc vs the bulk density value of 0.957 g/cc. That figure of 0.957 g/cc is the value I measured for my lot of Reloader-22.
 
Next is the bullet modification page.

 
It is here that you can change the values for the dimensions of a given bullet, or create your own. Since the lot of Sierra 220 BTSP that I have do not differ in measurement from the QL nominal figures, I have not changed anything on this page. However, I have several bullets that differ significantly from the QL nominal figures. I have a special file for those. Note the specifics about the boat-tail dimensions. It is from these that the volume of space in the case that the seated bullet occupies is calculated.
 
Next are pages for modifying or creating a case. In this example, this is the case I created for the 8mmx.376 Steyr. The dimensions here are right from a case fired in the chamber of the rifle.

 
Here is the page that opens when the "Cross-sectional Bore Area" button is pushed:

 
Cross-sectional area of the bore is an important variable in the calculation of chamber pressure, muzzle velocity, and barrel timing.
 
Here is the page that opens when the "Case Capacity, Overflow" button is pushed. It is here that the case capacity values we are discussing in this thread get set.

 
Here is the output for this case, with this bullet, seated this deep, in this barrel, using this powder:

 
and

 
There's lotsa info available, but in order to get anything other than what you would get from a reloading manual, you have to get specific measurements. If you do, it's kinda scary how close QL can get to reality.
 
This is NOT a sales pitch for QL. I actually think it would be WAY more than most folks need if htey're just trying to develop loads. However, I like to "fiddle", but more importantly, I like to make wildcats. For the serious wildcatter, I think QL is just about a "must have".
 
Paul