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)

  • Tailgunner

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    Jeff, good point. I think there is no “ideal” formula in reloading. Straight vs necked. Fast powder vs slow. Max velocity vs target load. Pistol vs rifle. Heavy bullet vs light. 9mm vs 44 magnum. All effect load “formula”. Otherwise I would not have a huge reloading spreadsheet. Always start from manufacturer’s load data.

    Reply

  • Roger Pankey

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    The best thing is to go by the power manufacture’s recommendations. They have spent a lot of money, time and engineering experimenting with pressure barrels and checking case pressures for all their bullets. I’m 69 and have been reloading since I was about twenty five for rifles, pistols and shotguns with no problem.

    Reply

    • Elton P. Green

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      The method for measuring case capacity is to fill the case to the rim with water. This gives the gram weight, which can be converted to grains. The reason water is used (and it has to be distilled pure water) is that a cc of water weighs exactly one gram. Powders weigh in by volume at different weights for one cubic centimeter, and so does every other substance. Water is used because it is a constant. For load density, I use a powder that has a burn rate that allows it to fill the case to about the shoulder to the neck area. A reloading manual will give a range of acceptable powders and starting charge weights/maximum charge weights. I pick two or three of the powders by Hodgden or IMR and Alliant which list charge weights that I know will fill a particular casing (30-06, 300 WM, .308 etc.) above the shoulder at maximum charge weights and then cut the charge by about 6%. Then we begin experimenting to see where the accuracy sweet spot for that cartridge is with the bullet weight desired, using each powder. Also, since the powders have different densities than water, load density for each powder has to be a volumetric measurement, since for example, 60 grains of IMR 4350 rifle powder has a greater volume than 60 grains of water. I believe that 4350 has a density of 0.78 or there abouts, so it takes up more volume for its weight. There’s a density table for various powders in the Lee Reloading Manual which give powder densities. Anyway, I use a volumetric measurement to determine load density with each given casing. As to the ‘right’ load density, I get better accuracy and less deviation in velocity if I have an 80 to 95 percent fill. I try to select powders which will give me the velocities, accuracy and pressures I want that will be within this range of volumetric fill. Also, I have found that extruded powders like H or IMR 4350 or 4831 have quite a bit of air space trapped between the kernels of powder. What may look like a 90% fill could be only 85%. I will use a funnel with an 8 inch tube to fill casings so that the powder can settle.

      Reply

  • Jeff Christen

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    Many magnum pistol cartridges are loaded very close to 100% when using spherical powders like H110 and W296. Accuracy with those loads is excellent. Are the straight walled cases exceptions?

    Reply

  • Terry

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    Powders have densities that range all over the map. Some are heavier than water and some are lighter than water. You have to convert the weight of the water to volume and then look at the volume your powder charge takes up. This should be close to 100% to maintain consistency in ignition.

    Reply

  • Brian Costello

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    That will not be accurate because the bullet seats well below the top of the case. The 100% mark that is the subject of the original post is when the powder is not compressed by the bullet. Furthermore, boat tail bullets are not flat so you cannot simply subtract the distance the bullet seats into the case. Even for a flat base bullet, if it seats deeper than the bottleneck, you cannot estimate the seating depth by filling to the bottom of where the bullet seats.

    Reply

  • Joseph fox

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    For me, a load must be at or better than 80% loading density. I prefer for the load to be at or near compressed. Some powders are position sensitive and this gets around the issue. If you point the barrel up and then lower it to a level shooting position and shoot versus lowering the barrel and then raising it to level can, with some powders, have and effect on the ignition. That’s going to effect pressure and accuracy. I avoid the issue by loading high density loads.

    Reply

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