How to measure blackpowder accurately? That’s an interesting question for all of us blackpowder shooters I think. And the answer is sometimes controversial. Some say measuring by weight is the only accurate way, and measuring only by volume is the evidence of a careless shooter. I believe that the truth is somewhere in the middle.
To have a clear view on this topic we first have to understand the working principles of the blackpowder. First of all blackpowder is not a compound but a mix of various ingredients like coal, potassium nitrate and sulphur. The process of making granulated blackpowder did not change too much in the past centuries. The strength and quality of the powder will depend on the quality of the ingredients, the mixing ratio, and size of corns.
The black powder particles do not explode but burn on the outer surface, while large amount of gases are generated. Therefore the more surface you have, the more gas the charge generates. So if you measure by volume and replace the 2Fg powder with 3Fg powder using the same volumetric measure you will have more gas, more pressure, and higher muzzle velocity.
The weight of the powder can change in time. It can absorb moisture from the air, so the particles will be heavier than when you first opened the box. So if you only rely on the scale, your volume can be different in June, than it was in February from the same box of powder. And more volume means more particles, more particles mean more morning surface, and more burning surface means more gases, higher pressure and higher muzzle velocity. So the question is obvious: should we just forget the scales and stick with volumetric measures?
The answer is simply no, because measuring by volume can be inaccurate. If you use ladle style measure, the charge will depend on how the powder settles. If you use a bench mounted volumetric measure the charge will also change depending on how much powder you have in the container. If you use a powder flask, the same thing happens: the more powder you have in it the more it will compress the charge in the spout. In this case it also matters how strong you push your finger on the mouth of the spot: the volume will be reduced if the finger pressure is harder.
My method for having consistent loads is the following:
1st Always use your volumetric measure to fill 5 of your vials.
2nd Weight these charges on a traditional scale and determinate the average.
3rd Now use your volumetric measure to weight your charges but check each of them on the scale as well. You can use any digital or analogue scales, but avoid the cheap low quality ones, stick with scales designed for weighing powder.
4th Add or remove some powder is necessary to have exactly the average load weight. A trickler is a great help in this job.
This method guarantees you will have the equal volume, and measuring all charges by weight as a second step is used to check the consistency of the work.
This method offers exceptional accuracy regardless of the season, but I also have to tell you that I only use this method for the most important occasions. But remember: the volumetric measure is the key of the project not registering the weight of the charge. For everyday practice and fun shooting I stick with skipping the scale check part of course.