Reloading: Load Density

By Bob Campbell published on in How To, Reloading

The load density formula has provided excellent results for handloaders for many years. The main reason is simply that the load density formula works without fail. Eighty-five percent density is just about ideal, but let’s look at how reloaders have come to that number.

Lyman 50th reloading manual

Obtaining several handloading manuals is a must.

Density is simply the ratio of the cartridge case capacity and the actual amount of the case filled by powder. Pulling and checking some of our more accurate factory ammunition will show a density of 80 to 90 percent, so I am on the right track.

I do not like to use compressed charges. While I have done so, I cannot say the results have always been good. The reason we do not attempt 100 percent density is because there must be room for igniting flame from the primer to move across the powder charge. A compressed load would retard this action.

While I have no proof, many experienced riflemen believe a compressed charge leads to excess heat and barrel wear. By the same token, a powder charge weight that is of small density can come under what is called detonation. This is a tremendous pressure spike and should be avoided. Too much air space is the culprit of detonation, which has been known to occur even in revolver cartridges.

Calculating load density is simple, but you have to know the cartridge case capacity first. There are various methods of figuring cartridge case capacity, but many are flawed. I do not think measuring capacity by filling an empty case is relevant. I use a dummy case—with the bullet I intend to use properly seated—and weigh the case. Next, I fill the case with water through the primer pocket hole by using some type of needle or a small jet of some type. I weigh the case when filled with water, after capping the base.

Let’s say that the water capacity is 50 grains. A 40-grain powder charge would represent an 80 percent capacity of the case. Therefore, the powder charge would represent 80 percent loading density. It is seldom so cut and dry, but this is how powder capacity is measured. While this formula differs from the recommendations of those who have experience with many types of powders, in my experience it works, and it is the type of scientific notation used by factory ballisticians.

Once you have searched the loading manuals, you can narrow the choice down to several promising powders. A great boon to the aspiring handloader is the new sample pack offered by Hodgdon. This pack features small canisters of several powders and is available in a ‘varmint’ version. This is simply among the finest new products I have seen offered to experimental handloaders in some time. Again, I don’t run my handloads wide open. There are differences in performance in cold or hot weather. A load skirting on the edge just may not be completely safe in all environmental situations.

What load density formula do you find delivers the best results? Share your answer in the comment section.

SLRule

Bob Campbell is a former peace officer and published author with over 40 years combined shooting and police and security experience. Bob holds a degree in Criminal Justice. Bob is the author of the books, The Handgun in Personal Defense, Holsters for Combat and Concealed Carry, The 1911 Automatic Pistol, The Gun Digest Book of Personal Protection and Home Defense, The Shooter’s Guide to the 1911, The Hunter and the Hunted, and The Complete Illustrated Manual of Handgun Skills. His latest book is Dealing with the Great Ammo Shortage. He is also a regular contributor to Gun Tests, American Gunsmith, Small Arms Review, Gun Digest, Concealed Carry Magazine, Knife World, Women and Guns, Handloader and other publications. Bob is well-known for his firearm testing.

View all articles by Bob Campbell

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Comments (20)

  • Lloyd

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    If we are talking about 80 percent of case capacity, why not just take a fired case with the spent primer still in and fill the case with whatever powder you are interested in using then dump the powder and weigh it. Calculate the weight and load it with 80 percent of that weight. Maybe that is too simple, I don’t know if that will accurately determine the volume but is seems to me it would.

    Reply

  • Tim Ferrall

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    Correct me if I am wrong, but SAAMI specs are for the OUTSIDE of a cartridge, not the inside, so load density with a specific charge of any powder will be dependent on the internal capacity of the case. This can vary from lot to lot, and brand to brand. Since brass cases can, and will, lengthen after each firing, and must be trimmed to length, the internal volume will change as the brass gets thinner. The most important thing for any reloader is the caption on the photograph at the top of this article: Get several good loading manuals, and USE THEM! Nowadays, reputable manufacturers of powder, bullets, and reloading supplies put their data online. Detonation can be a problem with black powder if there is space between the powder and projectile. A well-known ammo company uses a low bulk density on their .470 Nitro Express cartridges without a filler wad to hold the powder against the primer. Anyone who has ever used Bullseye powder knows that the loading density can be around 30%. Absent a need to shoot miniscule groups in a bench rest competition, load density is not all that important.

    Reply

  • Brian Costello

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    I agree with Mr. Brown, and not just we have the same first name. The only way water would work as a substitute for powder is if they had the same density which they most certainly do not. Water can only provide the volume of the inside of the case but we do not measure the volume of powder. If I were going to measure the loading capacity of a cartridge, I would de-prime a spent case then drill out the primer pocket with a drill about the same diameter or slightly bigger than the primer, seat the bullet in question, then fill the cartridge from the bottom with a very small funnel. Cone shaped paper water cups work well for this since you can cut as small of a hole in the bottom as needed. Fill up to the bottom of the nice and shiny brass rim inside the pocket. That charge can be weighed and used to see what the full capacity of the case is. This also allows easy removal of the bullet so it can live to fly another day and the case can be re-used for other bullet types.

    Reply

  • mark

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    I agree with Brian and Jim. However, as Jim states, some sort of accurate way of a volume measure would work.

    Reply

  • Dr.Hess

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    I’m with Jim and Brian here. Density of water is not the same as density of powder.

    What you could do, Bob, is: Take an empty, fired case. Weigh it. Fill it with water to the top, or to some mark made on the inside. Weigh it (without spilling). Empty it, dry it, fill it to the same level with the specific powder you are going to load with. Weigh it. Now, after some maffs, the ratio of the water to the powder weights can be used with your previous weight of the water in an empty case with seated bullet to give you the weight of the equivalent powder for 100% capacity.

    Reply

  • Mike

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    I measure case powder volume with powder. Drill out the flash hole in your test case. Seat your bullet then fill it with the powder. Weight the powder.

    Reply

    • Bruce

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      Absolutely right, Mike. Using water is as preposterous as using liquid mercury! The density difference (water vs. propellant) is just too significant. Maybe Bob Campbell had been drinking some FIREwater when he developed his case volume estimator.

      Reply

  • Secundius

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    The German produced a Sniper Cartridge for the 98k Mauser, called the 7.92×57 Nahpatrone (Near Cartridge), Which had a 0.55-grain Propellant Charge firing a 128-grain FMJ Spitzer to a maximum muzzle velocity of ~260-meters/second, to a range of ~300-meters. Used with HUB-23 Suppressor it was Virtually Silent. An added touch, was that the Germans used “Yankee Candle” Propellant which left NO Smell when fired, giving the Snipers position away…

    Reply

  • Illanoyed

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    Am new to reloading – thank you for sharing the wisdom and techniques!

    Reply

  • Tail Gunner

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    I do not exceed 80% in pistol loads. With fast powder, 65% is the lower limit.

    Reply

  • Brian Brown

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    Bob,

    I’m a bit speechless at the method that you’ve outlined above. No disagreement on the 85% capacity being a good rule of thumb for the sweet spot, but you can’t equate water and powder by weight, and then assume that they occupy the same volume. That is very, very wrong…especially when using a coarse-grained or stick powder.

    Do this: Take a fired case, doesn’t really matter what caliber. Leave the spent primer in, to seal the flash hole and weigh it to get the empty weight. Fill the case completely with water and weigh it again, to get the weight of the water. Let’s say, for sake of discussion, that the case holds 50gr of water. Now dump the water from the case and dry it out to make sure no water remains. Measure out 50 grains of something like IMR 4064 and try to fit it in your case. I guarantee you, it will not fit. And if you use your formula above and try to fit 40 grains, you might get it in there…maybe. It still may not fit, but even if it does you are likely outside of that 80-90% window that you’re talking about.

    Obviously, with a finer-grained powder like the Winchester ball powders, that will come closer to matching your water measurement. But many powders do not, and the method you’ve outlined isn’t a valid one to use.

    Reply

    • Jim in Conroe

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      I have to agree with Brian. Using weight of water as equivalent to a weight of powder is like equating 1 lb of lead to 1 lb of feathers. What you need is not a density measure, but a volumetric measure.

      My suggestion would be to load an empty case with the desired charge of powder, then measure the distance from the top of the cartridge less the seating depth of the bullet to the top of the powder charge. Then calculate the empty volume of the case with the bullet seated. These measurements will not be precise, since the volume of the case needs to take into account case wall thickness and the volume of the neck on a necked cartridge. Still, the errors should be about the same for both measurement.

      Then, you are in a position to calculate the ratio of the volume occupied by the powder to the volume of the empty cartridge with the bullet seated.

      Reply

    • Mike

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      I was going to write an extended reply but Mr Brown pretty well covered it. You also stated that ballisticians use the water to powder method. I find it impossible to believe that so technically oriented individuals would do such a thing. Have to compare apples to apples.

      Also, in my experience, 80% of capacity is a good starting point for load development but, generally, near 100% capacity is where I find my most accurate loads.

      Reply

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