A common yet technical question that everyone asks is “What is the best way to measure gun powder?” While some never measure the volume, they like weighing it on a scale in grains. However, the importance of knowing the volume in a load is critical but it’s near impossible to adjust precisely.
The density of the powder changes overtime and that is the general theory. The powder absorbs moisture and that is why volume provides consistency. Meaning – A steadier total gun powder dose than weight.
You may also have read that because of the shape of the grains (greater space between them) the light charge of a particular volume is light. This increases the burning speed as the flame moves through them quicker. Think of it as a fast burning gun powder, the fast burning gun powder (during a certain peak pressure) have a decreased maximum charge weights. Being lighter and faster, any charge which allows more space between the grains would be recompensing for the change of pressure – to some extent.
For compressed loads, the grains have lesser space between them and are tightly packed. Would a partially filled case be prone to vibration? The volume variation may be a determining factor for bench-rest shooters who lets the vibration settles the powder with an uncompressed load.
Back to the moisture content theory, weight and drop tube dispensed or vibration-settled volume will usually correspond well with uncompressed loads (during any loading session). The weight is also more accurate for flake and stick gun powders, the reason is simple, you will finish before the moisture gets to your gun powder and changes it weight. Many people do a volume measure if they feel that the gun powder density is changing between loads, they also weigh the charge before the loading and then simply use the average as an adjustment.
There is much confusion about gun powder that needs to be made clear. When we say “How to measure gun powder?” do we mean “weigh?” or “volume?” If we are saying “weigh” then we are definitely talking about smokeless propellants while black gun powder is usually measured by volume.
The powder measure is a common apparatus used by reloaders the apparatus measures smokeless powder by volume. The same should not be applied with black gun powder. There are two ways by which the powder gains its reference to weight and is measured.
Most manufacturers provide a burn rate chart with gives information on the charges by weight comparative to a measure cavity of a certain volume. The charts are an important tool which helps user determine the solution that works for them, unfortunately, there is no exact or approximate figure when talking about volume and weight. In fact, this is a very tricky subject and mostly determined by the user.
The use of a quality calibrated gun powder scale is the second method; you may have read or heard many debates about gun powder charges “+/- .1 gr.” But that is a very small amount and that is why a scale is your best friend.