According to Wikipedia, “Load density is the percentage of the space in the cartridge case that is filled with powder. In general, loads close to 100% density (or even loads where seating the bullet in the case, compresses the powder) ignite and burn more consistently than lower-density loads.” I’ll agree with that, but a bit more information needs to be added to clarify one important point.
The definition above states “cartridge case”. This needs definition in and of itself. A cartridge case is just that and no more. No primer, no powder and no bullet. A cartridge, on the other hand, is a complete loaded round of ammunition.
When handloaders are speaking of ‘COL’ or ‘Cartridge Overall Length’, It’s generally understood that the length of a loaded cartridge is being referred to. However, this mysterious load density term has been interpreted to mean two entirely different things. If one is not completely clear on the difference between case density and load density, it could mean the difference between a successful load development and the firearm going to autodestruct.
Here it is: Case Density is the amount of powder a case will hold when it is completely full with no bullet in it. Imagine a 5 gallon bucket completely full of water. If the water measures out to 5 gallons and 3 1/2 ounces, that’s the case density.
Load Density is the amount of powder compared to the space available with the bullet seated in the case. Go back to the bucket of water. Push a basketball into the bucket so that half of the ball is in the bucket. It will displace some of the water and make it overflow. When you take the ball out, there’s less water in the bucket. That would be 100% load density with the basketball ‘seated’ in the bucket.
Why all the splitting hairs over semantics? Because sometimes a couple of grains of powder can cause the pressure in a cartridge to spike. If the pressure spike is high enough, it can cause the firearm to structurally fail and explode. I don’t care how handsome you think you are, you won’t look sharp with a rifle bolt in your face.
Now that I have beaten that horse to death, we can move on to the why of establishing load density. Go back to the definition in the first paragraph and read it again. After all, if the ammunition is not accurate, it’s useless.
Generally speaking, the slower powders, especially the stick type rifle powders, will be what most handloaders will choose for full power charges in rifle calibers. As mentioned, theoretically, the closer the charge gets to 100% load density, the more accurate is the ammunition.
There’s another really good reason to understand load density and know how to establish it. I have several 7 pound jugs of powder that is not commercially manufactured. It’s a tubular stick powder identified as IMR 7383. 7383 is a military surplus powder that can be used in a wide range of calibers at full power. However, it has a very bad habit of spiking when loaded beyond 90 to 95% load density.
Knowing that 7383 is quirky and tends to spike, it’s critical that the hand loader start load development somewhere below 100% load density with this powder. It’s been my experience with this powder that 95% is a good density to start with in medium size calibers. 243, 308, 30-06, 303 and 8MM are good examples of medium calibers.
One method used to establish 100% load density is to place a bullet next to an empty case with the bullet located as it would be when seated and mark the case at the bottom of the bullet.
Powder is then poured into the case until the level is at the mark. The down side of this method is the hand loader has nothing to refer to inside the case to match the level of the powder to. At best, one can guess that it’s close.
I have developed a method that gives the hand loader a way of judging the amount of powder more accurately. I start by seating a bullet to the desired COL in an empty, unprimed case. The case is clamped in a wood lined carpenter’s vise on a horizontal axis.
If you don’t have such a vise, two strips of wood can be used, one on each side of the case. It’s important the web of the case be firmly secured but the case not be crushed.
The primer pocket is then drilled through with a bit at least the diameter of the pocket, if not larger. I have used a 1/4″ bit, but that’s about as big as you would want to use.
When that’s done, take the case out of the vise and turn it mouth down to insure any shavings inside the case are out.
Put the drilled case back in the vise with enough of the case head exposed to get a charging funnel on it. Place the funnel over the case head and, using a small scoop, begin pouring powder into the case through the drilled out primer pocket. Check the level of the powder frequently to avoid over filling.
The object is to fill the case until the level of the powder is right up to the inside of the case web. The hole allows you to see exactly where the powder is and the inside of the case web gives you a defined line to fill to.
Remove the filled case carefully to avoid spilling the powder. The quantity of powder is critical. Set up a scale with a powder pan, pour the powder into the pan and make sure you got every bit of the powder out. I usually tap on the inverted case with a pencil or some such to achieve this. Record the weight of the powder in the pan. That is the 100% load density for the cartridge, bullet and COL you have chosen.
Depending on several factors, powder chosen, max load suggested, velocity desired and so on, this data you have established can be used in your load development.
As always, use common sense and good safety practices, refer to your manuals and THINK. Loaded ammunition can be defined as controlled explosive devices. An uncontrolled explosive device will kill you.