Reloading: Powder Charging Technique

What does a spoonful of powder weigh? Indeed, what’s the volume of a spoonful? Yeah right, they’re pretty dim questions. So what does a cubic centimetre of Reloader 7 weigh? That may sound more sensible - but is it? We first looked at this topic about a year ago as part of the huge subject that is measurement. Most loading manuals simply quote a weight for each powder choice. Traditional powder ‘measures’ measure by volume but other than the Lee Perfect Measure and a couple of others, they are generally not calibrated to read actual volume. Uniquely, Lee market their comprehensive sets of dippers calibrated in cubic centimetres (cc s). However, ensuring a consistent and accurate weight for each charge is not as simple as it may seem.

Weights, Measures and Densities

When we charge a case with propellant we’re actually installing energy in the form of calories. But here’s the problem; that energy comes in a multitude of shapes and sizes. EVEN within the same tub there can be subtle variations. If you’ve used more than one type or brand then you’ll see what I mean. This is further compounded by the fact that almost every make of propellant has a slightly different calorific density… giving you more or less bang for the cubic centimetre. We’ve previously discussed the way in which the shape of the flakes or grains plays a part in the rate of deflagration (burning); however, they can also affect their ability to be accurately measured.

As a simple demo, upset your wife by putting a brace of mugs on the worktop. Pour uncooked long-grain rice (to simulate ball powder) into one until it is level with the rim. Now pour corn flakes (simulates a coarse flake powder) into the other until level with the rim. Pick up both cups and tap the bottoms on the worktop to settle the contents. Yeah, it’s pretty obvious. The point it makes is that coarse flake powder will continue to compact in the powder measure for dozens of cycles and again when you top up. For a set volume it means that each thrown charge will get heavier as the packed density increases.

Traditional Values

So let’s go back to basic instructions. When using a conventional powder measure make sure that the hopper is regularly filled, cycle the measure at least a dozen times before you even bother to weigh the first sample. Then continue to cycle, weigh, adjust and re-weigh until the readings become consistent. When refilling an empty hopper or adding powder from a different lot number, go through all the check processes again. For reliable and accurate charging the easiest method is to throw a slightly underweight charge into the pan on either your beam balance or electronic scale and then increase the weight a flake, kernel or ball at a time with a powder trickler. If you’re using a beam balance, tap the beam and let it re-settle for best accuracy. If you get to almost the end of a tub and the residue seems to include more coating dust and fines than usual – do one of two things. Pour it on the rose garden or add it to the next tub of the same type and carefully mix it in.

Dipping a Volume

Black powder dippers had been around since almost the beginning of shooting… it was an easy ‘in the field’ means of measuring a charge. However, at the advent of nitrobased reloading dipper users were issued with a dire warning, “Use them and you’ll blow up your gun”. For shooters steeped in the use of black powder it was hard to come to terms with the huge variation in calorific density. Cow logic dictated that if your favoured dipper worked with black powder then it should work with this new nitro powder stuff!!!! Hmm.

Lee broke the mould with their comprehensive range of volumetric dippers about 30 years ago. The problem was the fact that, other than the charts issued with their dipper and die sets, all the published data referred to just charge weights. Richard Lee simply rewrote the rules for a loading manual, his Modern Reloading (now in Second Edition) including the volumetric conversion for each charge and where available, the appropriate Lee dipper number.

Margins of Error

The Lee dipper design has a fixed ratio between diameter and depth – Richard arguing that it is designed to give the smallest volumetric variation between a heaped measure and a level one. He quotes the extreme variation as between 7 and 12%. I accept that any handloader would have to be terminally incompetent to work with such a wide variation. However, using the suggested method of dipping firmly into the powder tub and then using a card to scrape the surface flush, (à La Guinness froth) reduces the margin for error to a volumetric variation of up to 2 or 3% depending upon the nature of the granules. That would equate to around 7 tenths of a grain in my 300yd Long Range revolver load of 22gns. It’s safe, but ten times my acceptable error. That said, for the rapid assembly of plinking loads the dipper principle does work well enough.

The average powder measure operates in a similar way to the card scraping dipper process – the barrel rotating in its body to ‘scrape’ a level surface in the measure. Where it gains is the fact that the powder in the reservoir is (should be!) under a more constant compression load… density. From limited experiments I would estimate the results are generally better than 1%.

For most of the weighing devices the margin of error is a more or less fixed amount. Electronic scale makers often quoting better than 0.025 of a grain and beam scale makers claiming better than 0.1gn. However, many of the best beam devices can be made to deliver 0.05gn accuracy with patient and consistent operation. The rule is a simple one; correctly weighed charges will always be more accurate than volumetric ones.