Author Topic: Calculating load density? (Read 1766 times)

B. Miville · « **on:** July 20, 2008, 02:35:12 AM »

Hey folks,

I was wondering if anyone, off hand, knew how to calculate the load density for a cartridge? I have a table listing powder VD, I found a site that lists general cartridge capacity in CC, and I have trying to toy with calculating load densities...but failing. So can anyone tell me how to do this, or do they know of an online calculator for it (I tried Google, but a search produced nothing).

Brian

Lone Star · « **Reply #1 on:** July 20, 2008, 03:54:34 AM »

It is not possible to be too accurate with any calculator if you use the density of the powder. Different powder grain shapes mean a different amount of air space between the grains for different powders - spherical powders will pack tighter than log-grained powders for example. If you can get the bulk density of each powder in grams/cc then you can calculate the load density....kinda. This will change with different bullet weights in the same cartridge, so almost no matter what you do you are only extimating load density. It just depends on how accurate you want to be. Nosler explains what they do in their manuals - it is just a relative estimate.

.

B. Miville · « **Reply #2 on:** July 20, 2008, 06:01:45 AM »

Quote from: Lone Star on July 20, 2008, 03:54:34 AM

It is not possible to be too accurate with any calculator if you use the density of the powder. Different powder grain shapes mean a different amount of air space between the grains for different powders - spherical powders will pack tighter than log-grained powders for example. If you can get the bulk density of each powder in grams/cc then you can calculate the load density....kinda. This will change with different bullet weights in the same cartridge, so almost no matter what you do you are only extimating load density. It just depends on how accurate you want to be. Nosler explains what they do in their manuals - it is just a relative estimate.

.

Hey Lone Star,

Yes, I am only looking to be "in the ballpark". All I would like to do is, when looking at 3 or 4 powders that I consider "good prospects" for a new load, pick the one that comes closest to filling the case (though I understand plenty of other factors need to be considred....but this is just one more piece of info that could help make a decision.) You mention the Nosler manual, so I dug out my copy just now and found what you mentioned. It looks like a good start. I did read up a bit on VD and know that any given powder from a manufacturer can vary by as much as 10% per lot. A "very general" estimate is plenty good for me.

Thanks!

Brian

Lone Star · « **Reply #3 on:** July 20, 2008, 06:39:24 AM »

Then Nosler's method is probably just fine - it conforms to the KISS principal. . They fill the case with water and seat the particular bullet they will use. They weigh the water in the case in grains and divide that vaule into the grains of powder used. This gives a relative rating of how well particular powders will fill a particular case under that bullet.

.

Graybeard · « **Reply #4 on:** July 20, 2008, 11:12:13 AM »

Fill the case with the powder of choice. Dump it into your scale pan and weight. Now you have a 100% number. Determine what percentage of that any given charge you throw of that powder using normal math. If you do things like swirling or vibration to allow the case to hold more than when normally filled to the top then that is a compressed load and density will be above 100%.

That's probably not precisely the way the load manual folks do it but is to me the most accurate way of doing it. Of course if you fill a case flush with the top of neck and just seat the bullet it will compress the powder so in effect you can call that a compressed load but if you vibrate it first and then seat the bullet most times you'll find it is not really compressed at all as the powder will settle to the point the bullet doesn't really contact it. Of course the more coarse the powder the more it will setting via vibration. Ball powders settle much less.

Now having said that why in the world you care is beyond me but if you do that's fine and I don't need to understand. I really think tho you are kidding yourself if you think it's a useful or valuable number to have. Just find a load that is accurate and don't worry about such minor nuances.

FW Conch · « **Reply #5 on:** July 21, 2008, 04:10:35 AM »

Yes - what Graybeard said ! I use my shell that is only sized 1/16" down the neck, put a bullet in it, ease it all the way in the chamber to determine how far out the lands are, then I know how far in or out the neck I can seat the bullet. The flash hole in the case is plugged so now I can remove the bullet, fill the case with powder up to where the bullet base stops, then weigh the powder & "CHECK" where it falls in the load data. It is the KISS method & it's not very sexy but it sure is effective. Some of my most accurate loads use fast burning powders & don't come anywhere near filling the case up anyway.

beemanbeme · « **Reply #6 on:** July 21, 2008, 05:55:46 AM »

I've never paid much attention to it as I prefer slow powders, but it seems somewhere in my misspent past I've read that a load density @80% or better works well. (it's one of the attractions of a compressed load) It seems that insures a substantial amount of powder against the primer and no thin spots or voids along the powder column to retard burning.
IMO, it's the sort of thing that folks with too much time on their hands think about.

(sorry miville)

Catfish · « **Reply #7 on:** July 21, 2008, 07:55:37 AM »

Load density is nothing to get hung up on. GB`s method of filling the case would be over 100% with most others defination because it will be compressed when a bullet is seated and most people figure 100% as when the case is full, without being compressed, and the bullet is seated. The same load in cases made by different manufactures will have a different load density because the case volumes will be different.

B. Miville · « **Reply #8 on:** July 21, 2008, 10:56:59 AM »

I realize it is not a major factor. I am just looking at it as one more piece to the puzzle. I am looking at it for powders I am considering, not have already. Since, at least for me, buying 3, 4 or 5 different powders just to work with one new load is not an option. So as you can see it would be impossible for me to "just fill up the case".

Brian

beemanbeme · « **Reply #9 on:** July 22, 2008, 06:09:43 AM »

Maybe an easier way to figure that out would be to go to your load book and look at each cartridge you're reloading for. Look at the powder that's half or two thirds of the way down the list (toward the slowest) See which of those powders your cartridges have most in common. Maybe??
What cartridges are you loading for?

B. Miville · « **Reply #10 on:** July 22, 2008, 12:33:29 PM »

Quote from: beemanbeme on July 22, 2008, 06:09:43 AM

What cartridges are you loading for?

.223, .30-06, .45 Colt, .257 Roberts, .45 ACP, .357 Mag, .38 Special,.40 S&W. Though this question was mostly pertaining to the rifle rounds (the pistol loads, except for the .45 Colt which is for a rifle, I have pretty much found good loads and have no need to go looking for new ones right now.)

Brian

fastbike · « **Reply #11 on:** July 23, 2008, 07:54:43 AM »

The one that comes closest to filling the cartridge will be the one that has the lowest density (lowest gram/cc or grains/cc). Takes more cc's to make a given charge weight. Not that hard for the relative comparison that you want.

Quote from: B. Miville on July 22, 2008, 12:33:29 PM

Quote from: beemanbeme on July 22, 2008, 06:09:43 AM

What cartridges are you loading for?

.223, .30-06, .45 Colt, .257 Roberts, .45 ACP, .357 Mag, .38 Special,.40 S&W. Though this question was mostly pertaining to the rifle rounds (the pistol loads, except for the .45 Colt which is for a rifle, I have pretty much found good loads and have no need to go looking for new ones right now.)

Brian

PaulS · « **Reply #12 on:** July 27, 2008, 01:06:47 PM »

Load density is the ratio of the weight of powder that is used in the load to the weight of water it takes to fill the case.
You need to find the weight of water that will fill the case then divide the weight of your powder charge by that weight.

75 grains of water
70 grains of powder
70 / 75 = 93.333% load density

75 grains of water
80 grains of powder
80 / 75 = 106.666% load density

Not all cases will hold the same amount of water - so weigh some water in your cases first.

Graybeard · « **Reply #13 on:** July 27, 2008, 01:55:43 PM »

Where in the world did you come up with that?

stimpylu32 · « **Reply #14 on:** July 27, 2008, 02:24:02 PM »

This may be what he is refuring to .

CALCULATING YOUR OWN LOAD DENSITIES

If you do not own software that will calculate load densities there is a manual method that will work. First it is necessary to determine the powder capacity of the cartridge. To do this, file a small notch inside the mouth of a fired but not decapped case so it extends from the rim of the case to a point just beneath the bullet's base when it is seated. Weigh the case and bullet. Fill the case with water and carefully seat the bullet while displacing water out the notch filed in the mouth. Weigh the water filled case and bullet again. The difference in weights is the powder capacity of the cartridge in grains of water.

Next, you must know the bulk density of the powder you are using. Some powder companies publish bulk densities, others force you to find the bulk density yourself. The bulk density of powder is most commonly expressed as grams per cubic centimeter (g/cc). Since the weight of one cc of water is nearly always 1 gram, a bulk density of 0.970 g/cc means the powder is 97% as dense as water. Bulk density is therefore also the powder's weight in any volume divided by the weight of water filling the same volume. To find the bulk density for a powder first weigh a container (large as practical for your reloading scale) to determine it's weight. Then weigh it filled to the top with powder. Fill the empty container with water and weigh it again. Divide the weight of powder the container will hold by the weight of water it will hold. The result (1.000 or less) is the bulk density of the powder.

To finish the calculation use these formulae: Cartridge Cap. in gr. of H20 * Powder's Bulk Density = Cartridge's Powder Capacity Powder Charge in gr. / Cartridge's Powder Capacity = Load Density

The Sierra load manu is ideally suited for load density analysis because powder charges are arranged under an estimated velocity column. Select a velocity column that is close to what you hope to achieve and calculate the load densities using the indicated powder charges

http://www.shootingsoftware.com/loadens.htm

stimpy

PaulS · « **Reply #15 on:** July 27, 2008, 03:50:47 PM »

Actually I learned the formula back inthe early seventies When I found load densities over 100%.
I did the research and found the information and I hung onto it every since.
I had not seen the software and I have never used the formula to try to calculate a load (sounds risky).
I have, in the past, used it to catagorize loads but it doesn't seem to have any correlation to accuracy.

Graybeard · « **Reply #16 on:** July 27, 2008, 05:31:20 PM »

I'm sorry but water has absolutely NOTHING to do with load density. The example given by Stimpy is a very round about way to use water to aid in determining it but it is kinda silly in my mind to worry about water.

Ya know 100% is a kinda simple concept really. It means the case if FULL. Now you can look at full from two perspectives one to the top of the mouth or to where ever the base of the bullet will be. There really is no way to be absolutely precise in the latter so I personally chose the former. It just so happens my method in my experiments fits really well with the load density numbers given in the few manuals that give it. Might be the other would also as there is for the most part not a great deal of difference in volume of the two but at least one is precisely measureable the other less so.

As I've already said it's nothing more than an exercise in futility anyway as it has no real world meaning. You might find a load with 60% load density is the most accurate one you can come up with or it might be one with 105% or anywhere in between. The only thing that really matters is what is a. most accurate or b. highest velocity or c. best combination of the two.

Load density tells you neither of those.

PaulS · « **Reply #17 on:** July 28, 2008, 08:48:38 AM »

Bill,
100% is a very simple concept. A full case is a full case.
If you fill a case with one powder it may weigh more or less than if you fill it with another powder.
Load density has to take into account the specific gravity of the powder.
The specific gravity of smokeless powders ranges from 0.6 to 1.65.
a case full of one powder might therefore have a load density of 0.6 and with another powder it might have a load density of 1.65 or somewhere in between.

You are absolutely right - it has no real world application.
It is a scientific term that relates the weight of the powder charge volume with the "standard weight volume" of the case.
In scientific circles the "standard weight volume" is water because as defined it has a specific gravity (density) of 1.0000.
That is why water weight is the standard of case weight volume capacity.

For most reloaders (myself included) there are few uses for knowing the load density of a given load - I just tend to be a bit anal about terminology and its definitions.

I hope that my explaination has helped others understand the term

Graybeard · « **Reply #18 on:** July 28, 2008, 09:47:44 AM »

We're just gonna hafta agree to disagree on this one. I do not think you'll ever find a source to back your assertions. I think that 105% is about the highest load density I've ever seen posted. Water has no bearing. If you wish to continue to believe it does feel free just don't expect to convince me of your error.

PaulS · « **Reply #19 on:** July 30, 2008, 10:24:10 PM »

Bill,
I have no problem agreeing to disagree.
I would like you to explain this one example with your method of load density:
a 30-30 Win. using a 150 gr. bullet with the following recommended maximum loads from the Hodgdon 25th powder data manual:
33 grains of H322
39 grains of H414

H332 has a specific gravity of 1.1 (according to Hodgdon's website)
H414 has a specific gravity of 1.6 (according to Hodgdon's website)
30 grains of H332 takes up 1 cc of space
24.38 grains of H414 takes up the same space
That means that the H332 fills only the same weight as 1.1 CCs of water in the case while the H414 fills the same weight as 1.6 CCs of water in that same case.
If they fill the same volume in the case which one has the higher load density and why?